Low-carbon power is electricity produced with substantially lower greenhouse gas emissions than conventional fossil fuelpower generation. The energy transition to low-carbon power is one of the most important actions required to limit climate change. Power sector emissions may have peaked in 2018. During the first six months of 2020, scientists observed an 8.8% decrease in global CO2 emissions relative to 2019 due to COVID-19 lockdown measures.
The two main sources of the decrease in emissions included ground
transportation (40%) and the power sector (22%). This event is the
largest absolute decrease in CO2 emissions in history, but
emphasizes that low-carbon power "must be based on structural and
transformational changes in energy-production systems".
Low carbon power generation sources include wind power, solar power, nuclear power and most hydropower. The term largely excludes conventional fossil fuel plant
sources, and is only used to describe a particular subset of operating
fossil fuel power systems, specifically, those that are successfully
coupled with a flue gascarbon capture and storage (CCS) system.
Globally almost 40% of electricity generation came from low-carbon
sources in 2020: about 10% being nuclear power, almost 10% wind and
solar, and around 20% hydropower and other renewables.
History
Percentage of electricity generation from low-carbon sources in 2019.
During the late 20th and early 21st century significant findings regarding global warming highlighted the need to curb carbon emissions. From this, the idea for low-carbon power was born. The Intergovernmental Panel on Climate Change (IPCC), established by the World Meteorological Organization (WMO) and the United Nations Environment Program
(UNEP) in 1988, set the scientific precedence for the introduction of
low-carbon power. The IPCC has continued to provide scientific,
technical and socio-economic advice to the world community, through its
periodic assessment reports and special reports.
Internationally, the most prominent early step in the direction of low carbon power was the signing of the Kyoto Protocol,
which came into force on 16 February 2005, under which most
industrialized countries committed to reduce their carbon emissions. The
historical event set the political precedence for introduction of
low-carbon power technology.
On a social level, perhaps the biggest factor
contributing to the general public's awareness of climate change and
the need for new technologies, including low carbon power, came from the
documentary An Inconvenient Truth, which clarified and highlighted the problem of global warming.
Power sources by greenhouse gas emissions
Life-cycle greenhouse gas emissions of electricity supply technologies, median values calculated by IPCC
Life cycle CO2 equivalent (including albedo effect) from selected electricity supply technologies according to IPCC 2014.Arranged by decreasing median (gCO2eq/kWh) values.
Differentiating attributes of low-carbon power sources
Low carbon electricity generation percentage worldwide by source
There are many options for lowering current levels of carbon
emissions. Some options, such as wind power and solar power, produce low
quantities of total life cycle carbon emissions, using entirely
renewable sources. Other options, such as nuclear power, produce a
comparable amount of carbon dioxide emissions as renewable technologies
in total life cycle emissions, but consume non-renewable, but
sustainable materials (uranium). The term low-carbon power
can also include power that continues to utilize the world's natural
resources, such as natural gas and coal, but only when they employ
techniques that reduce carbon dioxide emissions from these sources when
burning them for fuel, such as the, as of 2012, pilot plants performing Carbon capture and storage.
Because the cost of reducing emissions in the electricity sector
appears to be lower than in other sectors such as transportation, the
electricity sector may deliver the largest proportional carbon
reductions under an economically efficient climate policy.
Technologies to produce electric power with low-carbon emissions
are in use at various scales. Together, they accounted for almost 40% of
global electricity in 2020, with wind and solar almost 10%.
Technologies
The
2014 Intergovernmental Panel on Climate Change report identifies
nuclear, wind, solar and hydroelectricity in suitable locations as
technologies that can provide electricity with less than 5% of the
lifecycle greenhouse gas emissions of coal power.
Hydroelectric power
The Hoover Dam
when completed in 1936 was both the world's largest electric-power
generating station and the world's largest concrete structure.
Hydroelectric
plants have the advantage of being long-lived and many existing plants
have operated for more than 100 years. Hydropower is also an extremely
flexible technology from the perspective of power grid operation. Large
hydropower provides one of the lowest cost options in today's energy
market, even compared to fossil fuels and there are no harmful emissions
associated with plant operation. However, there are typically low greenhouse gas emissions with reservoirs, and possibly high emissions in the tropics.
Hydroelectric power is the world's largest low carbon source of electricity, supplying 15.6% of total electricity in 2019. China is by far the world's largest producer of hydroelectricity in the world, followed by Brazil and Canada.
However, there are several significant social and environmental
disadvantages of large-scale hydroelectric power systems: dislocation,
if people are living where the reservoirs are planned, release of significant amounts of carbon dioxide and methane during construction and flooding of the reservoir, and disruption of aquatic ecosystems and birdlife.
There is a strong consensus now that countries should adopt an
integrated approach towards managing water resources, which would
involve planning hydropower development in co-operation with other
water-using sectors.
Nuclear power, with a 10.6% share of world electricity production as of 2013, is the second largest low-carbon power source.
Nuclear power, in 2010, also provided two thirds of the twenty seven nation European Union's low-carbon energy, with some EU nations sourcing a large fraction of their electricity from nuclear power; for example France derives 79% of its electricity from nuclear. As of 2020 nuclear power provided 47% low-carbon power in the EU with countries largely based on nuclear power routinely achieving carbon intensity of 30-60 gCO2eq/kWh.
According to the IAEA and the European Nuclear Society, worldwide there were 68 civil nuclear power reactors under construction in 15 countries in 2013. China has 29 of these nuclear power reactors under construction, as of 2013, with plans to build many more, while in the US the licenses of almost half its reactors have been extended to 60 years, and plans to build another dozen are under serious consideration. There is also a considerable number
of new reactors being built in South Korea, India, and Russia.
Nuclear power's capability to add significantly to future low carbon
energy growth depends on several factors, including the economics of new
reactor designs, such as Generation III reactors, public opinion and national and regional politics.
In 2021 United Nations Economic Commission for Europe (UNECE) described nuclear power as important tool to mitigate climate change that has prevented 74 Gt of CO2 emissions over the last half century, providing 20% of energy in Europe and 43% of low-carbon energy.
In 2020, wind supplied almost 1600 TWh of electricity, which was over 5% of worldwide electrical generation and about 2% of energy consumption. With over 100 GW added during 2020, mostly in China, global installed wind power capacity reached more than 730 GW.
To help meet the Paris Agreement goals to limit climate change, analysts say it should expand much faster - by over 1% of electricity generation per year.
New onshore (on-land) wind farms are cheaper than new coal or gas plants, but expansion of wind power is being hindered by fossil fuel subsidies. Onshore wind farms have a greater visual impact on the landscape than other power stations, as they need to be spread over more land and need to be built in rural areas. Small onshore wind farms can feed some energy into the grid or provide power to isolated off-grid locations. Offshore wind farms
provide a steadier and stronger source of energy and have less visual
impact. Although there is less offshore wind power at present and
construction and maintenance costs are higher, it is expanding.
Wind power is variable renewable energy, so power-management techniques are used to match supply and demand, such as: wind hybrid power systems, hydroelectric power or other dispatchable power sources, excess capacity, geographically distributed turbines, exporting and importing power to neighboring areas, or grid storage. As the proportion of wind power in a region increases the grid may need to be upgraded. Weather forecasting allows the electric-power network to be readied for the predictable variations in production that occur.
The PS10 concentrates sunlight from a field of heliostats on a central tower.
Solar power is the conversion of sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power
(CSP). Concentrated solar power systems use lenses or mirrors and
tracking systems to focus a large area of sunlight into a small beam.
Photovoltaics convert light into electric current using the photoelectric effect.
Geothermal electricity is electricity generated
from geothermal energy. Technologies in use include dry steam power
plants, flash steam power plants and binary cycle power plants.
Geothermal electricity generation is used in 24 countries while geothermal heating is in use in 70 countries.
Current worldwide installed capacity is 10,715 megawatts (MW), with the largest capacity in the United States (3,086 MW), Philippines, and Indonesia. Estimates of the electricity generating potential of geothermal energy vary from 35 to 2000 GW.
Geothermal power is considered to be sustainable because the heat extraction is small compared to the Earth's heat content. The emission intensity of existing geothermal electric plants is on average 122 kg of CO 2 per megawatt-hour (MW·h) of electricity, a small fraction of that of conventional fossil fuel plants.
Tidal power
Tidal power is a form of hydropower
that converts the energy of tides into electricity or other useful
forms of power. The first large-scale tidal power plant (the Rance Tidal Power Station)
started operation in 1966. Although not yet widely used, tidal power
has potential for future electricity generation. Tides are more
predictable than wind energy and solar power.
Carbon capture and storage captures carbon dioxide from the flue gas
of power plants or other industry, transporting it to an appropriate
location where it can be buried securely in an underground reservoir.
While the technologies involved are all in use, and carbon capture and
storage is occurring in other industries (e.g., at the Sleipner gas field), no large scale integrated project has yet become operational within the power industry.
Improvements to current carbon capture and storage technologies could reduce CO2
capture costs by at least 20-30% over approximately the next decade,
while new technologies under development promise more substantial cost
reduction.
The Intergovernmental Panel on Climate Change
stated in its first working group report that “most of the observed
increase in globally averaged temperatures since the mid-20th century is
very likely due to the observed increase in anthropogenic greenhouse gas concentrations, contribute to climate change.
As a percentage of all anthropogenic greenhouse gas emissions, carbon dioxide (CO2) accounts for 72 percent (see Greenhouse gas), and has increased in concentration in the atmosphere from 315 parts per million (ppm) in 1958 to more than 375 ppm in 2005.
Emissions from energy make up more than 61.4 percent of all greenhouse gas emissions.
Power generation from traditional coal fuel sources accounts for 18.8
percent of all world greenhouse gas emissions, nearly double that
emitted by road transportation.
Estimates state that by 2020 the world will be producing around twice as much carbon emissions as it was in 2000.
World energy consumption is predicted to increase from 123,000 TWh (421 quadrillionBTU) in 2003 to 212,000 TWh (722 quadrillion BTU) in 2030. Coal consumption is predicted to nearly double in that same time. The fastest growth is seen in non-OECD Asian countries, especially China and India, where economic growth drives increased energy use.
By implementing low-carbon power options, world electricity demand
could continue to grow while maintaining stable carbon emission levels.
In the transportation sector there are moves away from fossil fuels and towards electric vehicles, such as mass transit and the electric car. These trends are small, but may eventually add a large demand to the electrical grid.
Domestic and industrial heat and hot water have largely been
supplied by burning fossil fuels such as fuel oil or natural gas at the
consumers' premises. Some countries have begun heat pump rebates to
encourage switching to electricity, potentially adding a large demand to
the grid.
Energy infrastructure
Coal-fired power plants are losing market share compared to low carbon power, and any built in the 2020s risk becoming stranded assets or stranded costs, partly because their capacity factors will decline.
Investment
Investment in low-carbon power sources and technologies is increasing at a rapid rate.
Zero-carbon power sources produce about 2% of the world's energy, but
account for about 18% of world investment in power generation,
attracting $100 billion of investment capital in 2006.
An influenza pandemic is an epidemic of an influenza
virus that spreads across a large region (either multiple continents or
worldwide) and infects a large proportion of the population. There have
been six major influenza epidemics in the last 140 years, with the 1918 flu pandemic
being the most severe; this is estimated to have been responsible for
the deaths of 50–100 million people. The most recent, the 2009 swine flu pandemic, resulted in under 300,000 deaths and is considered relatively mild. These pandemics occur irregularly.
Influenza pandemics occur when a new strain of the influenza
virus is transmitted to humans from another animal species. Species that
are thought to be important in the emergence of new human strains are
pigs, chickens and ducks. These novel strains are unaffected by any immunity
people may have to older strains of human influenza and can therefore
spread extremely rapidly and infect very large numbers of people. Influenza A viruses
can occasionally be transmitted from wild birds to other species,
causing outbreaks in domestic poultry, and may give rise to human
influenza pandemics. The propagation of influenza viruses throughout the world is thought in part to be by bird migrations, though commercial shipments of live bird products might also be implicated, as well as human travel patterns.
The World Health Organization
(WHO) has produced a six-stage classification that describes the
process by which a novel influenza virus moves from the first few
infections in humans through to a pandemic. This starts with the virus
mostly infecting animals, with a few cases where animals infect people,
then moves through the stage where the virus begins to spread directly
between people, and ends with a pandemic when infections from the new
virus have spread worldwide.
One strain of virus that may produce a pandemic in the future is a highly pathogenic variation of the H5N1 subtype of influenza A virus. On 11 June 2009, a new strain of H1N1 influenza was declared to be a pandemic (Stage 6) by the WHO after evidence of spreading in the southern hemisphere.
The 13 November 2009 worldwide update by the WHO stated that "[a]s of 8
November 2009, worldwide more than 206 countries and overseas
territories or communities have reported [503,536] laboratory confirmed
cases of pandemic influenza H1N1 2009, including over 6,250 deaths."
Structure of the influenza viron. The hemagglutinin (HA) and neuraminidase
(NA) proteins are shown on the surface of the particle. The viral RNAs
that make up the genome are shown as red coils inside the particle and
bound to Ribonuclear Proteins (RNPs).
Influenza, commonly known as the flu, is an infectious disease of birds and mammals.
It was thought to be caused by comets, earthquakes, volcanoes, cosmic
dust, the rising and setting of the sun, vapors arising from the air and
ground, or a blast from the stars. Now we know that it is caused by an RNA virus of the familyOrthomyxoviridae (the influenza viruses). In humans, common symptoms of influenza infection are fever, sore throat, muscle pains, severe headache, coughing, and weakness and fatigue. In more serious cases, influenza causespneumonia, which can be fatal, particularly in young children and the elderly. While sometimes confused with the common cold, influenza is a much more severe disease and is caused by a different type of virus. Although nausea and vomiting can be produced, especially in children, these symptoms are more characteristic of the unrelated gastroenteritis, which is sometimes called "stomach flu" or "24-hour flu."
Typically, influenza is transmitted from infected mammals through the air by coughs or sneezes, creating aerosols containing the virus, and from infected birds through their droppings. Influenza can also be transmitted by saliva, nasal secretions,
feces and blood. Healthy individuals can become infected if they
breathe in a virus-laden aerosol directly, or if they touch their eyes,
nose or mouth after touching any of the aforementioned bodily fluids (or
surfaces contaminated with those fluids). Flu viruses can remain
infectious for about one week at human body temperature, over 30 days at
0 °C (32 °F), and indefinitely at very low temperatures (such as lakes
in northeast Siberia). Most influenza strains can be inactivated easily by disinfectants and detergents.
Flu spreads around the world in seasonal epidemics. Ten pandemics were recorded before the Spanish flu of 1918. Three influenza pandemics
occurred during the 20th century and killed tens of millions of people,
with each of these pandemics being caused by the appearance of a new strain of the virus in humans. Often, these new strains result from the spread of an existing flu virus to humans from other animal species,
so close proximity between humans and animals can promote epidemics. In
addition, epidemiological factors, such as the WWI practice of packing
soldiers with severe influenza illness into field hospitals while
soldiers with mild illness stayed outside on the battlefield, are an
important determinant of whether or not a new strain of influenza virus
will spur a pandemic.
(During the 1918 Spanish flu pandemic, this practice served to promote
the evolution of more virulent viral strains over those that produced
mild illness.) When it first killed humans in Asia in the 1990s, a
deadly avian strain of H5N1 posed a great risk for a new influenza
pandemic; however, this virus did not mutate to spread easily between people.
Vaccinations against influenza are most commonly given to high-risk humans in industrialized countries and to farmed poultry. The most common human vaccine is the trivalent influenza vaccine that contains purified and inactivated material from three viral strains. Typically this vaccine includes material from two influenza A virus subtypes and one influenza B virus strain.
A vaccine formulated for one year may be ineffective in the following
year, since the influenza virus changes rapidly over time and different
strains become dominant. Antiviral drugs can be used to treat influenza, with neuraminidase inhibitors being particularly effective.
Variants of Influenzavirus A are identified and named according to the isolate that they are like and thus are presumed to share lineage (example Fujian flu virus like); according to their typical host (example Human flu virus); according to their subtype (example H3N2);
and according to their deadliness (e.g., Low Pathogenic as discussed
below). So a flu from a virus similar to the isolate
A/Fujian/411/2002(H3N2) is called Fujian flu, human flu, and H3N2 flu.
The various types of influenza
viruses in humans. Solid squares show the appearance of a new strain,
causing recurring influenza pandemics. Broken lines indicate uncertain
strain identifications.
Variants are sometimes named according to the species (host) the
strain is endemic in or adapted to. Some variants named using this
convention are:
Avian variants have also sometimes been named according to their deadliness in poultry, especially chickens:
Low Pathogenic Avian Influenza (LPAI)
Highly Pathogenic Avian Influenza (HPAI), also called: deadly flu or death flu
The Influenza A virus subtypes are labeled according to an H number (for hemagglutinin) and an N number (for neuraminidase). Each subtype virus has mutated into a variety of strains with differing pathogenic
profiles; some pathogenic to one species but not others, some
pathogenic to multiple species. Most known strains are extinct strains.
For example, the annual flu subtype H3N2 no longer contains the strain
that caused the Hong Kong Flu.
Influenza A viruses are negative sense, single-stranded, segmented RNA viruses. "There are 16 different HA antigens (H1 to H16) and nine different NA antigens
(N1 to N9) for influenza A. Until recently, 15 HA types had been
recognized, but recently two new types were isolated: a new type (H16)
was isolated from black-headed gulls caught in Sweden and the Netherlands in 1999 and reported in the literature in 2005." "The other, H17, was isolated from fruit bats caught in Guatemala and reported in the literature in 2013."
Nature of a flu pandemic
Some pandemics are relatively minor such as the one in 1957 called Asian flu (1–4 million dead, depending on source). Others have a higher Pandemic Severity Index whose severity warrants more comprehensive social isolation measures.
The 1918 pandemic killed tens of millions and sickened hundreds
of millions; the loss of this many people in the population caused
upheaval and psychological damage to many people.
There were not enough doctors, hospital rooms, or medical supplies for
the living as they contracted the disease. Dead bodies were often left
unburied as few people were available to deal with them. There can be
great social disruption as well as a sense of fear. Efforts to deal with
pandemics can leave a great deal to be desired because of human
selfishness, lack of trust, illegal behavior, and ignorance. For
example, in the 1918 pandemic: "This horrific disconnect between
reassurances and reality destroyed the credibility of those in
authority. People felt they had no one to turn to, no one to rely on, no
one to trust."
A letter from a physician at one U.S. Army camp in the 1918 pandemic said:
It is only a matter of a few hours then until death comes
[...]. It is horrible. One can stand it to see one, two or twenty men
die, but to see these poor devils dropping like flies [...]. We have
been averaging about 100 deaths per day [...]. Pneumonia means in about
all cases death [...]. We have lost an outrageous number of Nurses and
Drs. It takes special trains to carry away the dead. For several days
there were no coffins and the bodies piled up something fierce [...].
Wave nature
Flu
pandemics typically come in waves. The 1889–1890 and 1918–1919 flu
pandemics each came in three or four waves of increasing lethality. But within a wave, mortality was greater at the beginning of the wave.
Variable mortality
Mortality varies widely in a pandemic. In the 1918 pandemic:
In U.S. Army camps where reasonably reliable statistics
were kept, case mortality often exceeded 5 percent, and in some
circumstances exceeded 10 percent. In the British Army in India, case
mortality for white troops was 9.6 percent, for Indian troops 21.9
percent. In isolated human populations, the virus killed at even higher
rates. In the Fiji islands, it killed 14 percent of the entire
population in 16 days. In Labrador and Alaska, it killed at least
one-third of the entire native population.
Influenza pandemics
A 1921 book lists nine influenza pandemics prior to the 1889–90 flu, the first in 1510. A more modern source lists six.
The 1889–1890 pandemic, often referred to as the Asiatic flu or Russian flu, killed about 1 million people out of a world population of about 1.5 billion.
It was the last great pandemic of the 19th century, and is among the deadliest pandemics in history. The most reported effects of the pandemic took place from October 1889 to December 1890, with recurrences in 1891 to 1895.
The
difference between the influenza mortality age-distributions of the
1918 epidemic and normal epidemics. Deaths per 100,000 persons in each
age group, United States, for the interpandemic years 1911–1917 (dashed
line) and the pandemic year 1918 (solid line).
The Spanish flu pandemic lasted from 1918 to 1920. Various estimates say it killed between 17 million and 100 million people This pandemic has been described as "the greatest medical holocaust in history" and may have killed as many people as the Black Death, although the Black Death is estimated to have killed over a fifth of the world's population at the time,
a significantly higher proportion. This huge death toll was caused by
an extremely high infection rate of up to 50% and the extreme severity
of the symptoms, suspected to be caused by cytokine storms. Indeed, symptoms in 1918 were so unusual that initially influenza was misdiagnosed as dengue, cholera,
or typhoid. One observer wrote, "One of the most striking of the
complications was hemorrhage from mucous membranes, especially from the
nose, stomach, and intestine. Bleeding from the ears and petechial hemorrhages in the skin also occurred." The majority of deaths were from bacterial pneumonia, a secondary infection caused by influenza, but the virus also killed people directly, causing massive hemorrhages and edema in the lung.
The Spanish flu pandemic was truly global, spreading even to the Arctic
and remote Pacific islands. The unusually severe disease killed between
10 and 20% of those infected, as opposed to the more usual flu epidemic
mortality rate of 0.1%.
Another unusual feature of this pandemic was that it mostly killed
young adults, with 99% of pandemic influenza deaths occurring in people
under 65, and more than half in young adults 20 to 40 years old.
This is unusual since influenza is normally most deadly to the very
young (under age 2) and the very old (over age 70). The total mortality
of the 1918–1920 pandemic is estimated to be between 17 and 100 million
people, constituting approximately 1–6% of the world's population. As
many as 25 million may have been killed in the first 25 weeks; in
contrast, HIV/AIDS has killed 25 million in its first 25 years.
The Asian flu was a category 2flu pandemic outbreak of avian influenza that originated in China in early 1956 lasting until 1958. It originated from a mutation in wild ducks combining with a pre-existing human strain. The virus was first identified in Guizhou.
It spread to Singapore in February 1957, reached Hong Kong by April,
and US by June. Death toll in the US was approximately 116,000. The elderly were particularly vulnerable. Estimates of worldwide deaths vary widely depending on source, ranging from 1 million to 4 million.
The Hong Kong flu was a category 2flu pandemic caused by a strain of H3N2 descended from H2N2 by antigenic shift,
in which genes from multiple subtypes reassorted to form a new virus.
The Hong Kong Flu pandemic of 1968 and 1969 killed an estimated 1–4
million people worldwide. Those over 65 had the greatest death rates. In the US, there were about 100,000 deaths.
The 1977 Russian flu was a relatively benign flu pandemic, mostly affecting population younger than the age of 26 or 25. It is estimated that 700,000 people died due to the pandemic worldwide. The cause was H1N1 virus strain, which was not seen after 1957 until its re-appearance in China and the Soviet Union in 1977.
Genetic analysis and several unusual characteristics of the pandemic
have prompted speculation that the virus was released to the public
through a laboratory accident.
An epidemic of influenza-like illness of unknown causation occurred in Mexico in March–April 2009. On 24 April 2009, following the isolation of an A/H1N1 influenza in seven ill patients in the southwest US, the WHO
issued a statement on the outbreak of "influenza like illness" that
confirmed cases of A/H1N1 influenza had been reported in Mexico, and
that 20 confirmed cases of the disease had been reported in the US. The
next day, the number of confirmed cases rose to 40 in the US, 26 in
Mexico, six in Canada, and one in Spain. The disease spread rapidly
through the rest of the spring, and by 3 May, a total of 787 confirmed
cases had been reported worldwide.
On 11 June 2009, the ongoing outbreak of Influenza A/H1N1, commonly
referred to as swine flu, was officially declared by the WHO to be the
first influenza pandemic of the 21st century and a new strain of Influenza A virus subtype H1N1 first identified in April 2009. It is thought to be a mutation (reassortment) of four known strains of influenza A virus subtype H1N1: one endemic in humans, one endemic in birds, and two endemic in pigs (swine).
The rapid spread of this new virus was likely due to a general lack of
pre-existing antibody-mediated immunity in the human population.
On 1 November 2009, a worldwide update by the WHO stated that
"199 countries and overseas territories/communities have officially
reported a total of over 482,300 laboratory confirmed cases of the
influenza pandemic H1N1 infection, that included 6,071 deaths." By the end of the pandemic, there were more than 18,000 laboratory-confirmed deaths from H1N1.
Due to inadequate surveillance and lack of healthcare in many
countries, the actual total of cases and deaths was likely much higher
than reported. Experts, including the WHO, have since agreed that an
estimated 284,500 people were killed by the disease, about 15 times the
number of deaths in the initial death toll.
Other pandemic threat subtypes
"Human influenza virus" usually refers to those subtypes that spread widely among humans. H1N1, H1N2, and H3N2 are the only known Influenza A virus subtypes currently circulating among humans.
Genetic factors in distinguishing between "human flu viruses" and "avian influenza viruses" include:
PB2: (RNA polymerase): Amino acid (or residue) position 627 in the PB2 protein encoded by the PB2 RNA gene. Until H5N1, all known avian influenza viruses had a glutamic acid at position 627, while all human influenza viruses had a lysine.
HA: (hemagglutinin): Avian influenza HA bind alpha 2–3 sialic acid receptors while human influenza HA bind alpha 2–6 sialic acid receptors.
"About 52 key genetic changes distinguish avian influenza strains
from those that spread easily among people, according to researchers in
Taiwan, who analyzed the genes of more than 400 A type flu viruses."
"How many mutations would make an avian virus capable of infecting
humans efficiently, or how many mutations would render an influenza
virus a pandemic strain, is difficult to predict. We have examined
sequences from the 1918 strain, which is the only pandemic influenza
virus that could be entirely derived from avian strains. Of the 52
species-associated positions, 16 have residues typical for human
strains; the others remained as avian signatures. The result supports
the hypothesis that the 1918 pandemic virus is more closely related to
the avian influenza A virus than are other human influenza viruses."
Highly pathogenic H5N1 avian influenza kills 50% of humans that catch it. In one case, a boy with H5N1 experienced diarrhea followed rapidly by a coma without developing respiratory or flu-like symptoms.
The Influenza A virus subtypes that have been confirmed in humans, ordered by the number of known human pandemic deaths, are:
H1N1 is currently endemic in both human and pig populations. A variant of H1N1 was responsible for the Spanish flupandemic that killed some 50 million to 100 million people worldwide over about a year in 1918 and 1919. Controversy arose in October 2005, after the H1N1 genome was published in the journal, Science. Many fear that this information could be used for bioterrorism.
When he compared the 1918 virus
with today's human flu viruses, Dr. Taubenberger noticed that it had
alterations in just 25 to 30 of the virus's 4,400 amino acids. Those few
changes turned a bird virus into a killer that could spread from person
to person.
In mid-April 2009, an H1N1 variant appeared in Mexico, with its
center in Mexico City. By 26 April the variant had spread widely; with
cases reported in Canada, the US, New Zealand, the UK, France, Spain and
Israel. On 29 April WHO raised the worldwide pandemic phase to 5.
On 11 June 2009 the WHO raised the worldwide pandemic phase to 6, which
means that the H1N1 swine flu has reached pandemic proportions, with
nearly 30,000 confirmed cases worldwide.
A 13 November 2009 worldwide update by the UN's World Health
Organization (WHO) states that "206 countries and overseas
territories/communities have officially reported over 503,536 laboratory
confirmed cases of the influenza pandemic H1N1 infection, including
6,250 deaths."
The Asian Flu was a pandemic outbreak of H2N2 avian influenza that originated in China in 1957, spread worldwide that same year during which an influenza vaccine was developed, lasted until 1958 and caused between one and four million deaths.
H3N2 is currently endemic in both human and pig populations. It evolved from H2N2 by antigenic shift and caused the Hong Kong Flu pandemic of 1968 and 1969 that killed up to 750,000." An
early-onset, severe form of influenza A H3N2 made headlines when it
claimed the lives of several children in the United States in late
2003."
The dominant strain of annual flu in January 2006 is H3N2. Measured resistance to the standard antiviral drugs amantadine and rimantadine in H3N2 has increased from 1% in 1994 to 12% in 2003 to 91% in 2005.
[C]ontemporary human H3N2 influenza viruses are now
endemic in pigs in southern China and can reassort with avian H5N1
viruses in this intermediate host.
H7N7
has unusual zoonotic potential. In 2003 in Netherlands 89 people were
confirmed to have H7N7 influenza virus infection following an outbreak
in poultry on several farms. One death was recorded.
H1N2 is currently endemic in both human and pig populations. The new H1N2 strain appears to have resulted from the reassortment of the genes of the currently circulating influenza H1N1 and H3N2 subtypes. The hemagglutinin protein of the H1N2 virus is similar to that of the currently circulating H1N1 viruses and the neuraminidase protein is similar to that of the current H3N2 viruses.
No animal influenza virus circulating among animals have been reported to cause infection in humans.
Phase 2
An animal influenza virus circulating in
domesticated or wild animals is known to have caused infection in humans
and is therefore considered a specific potential pandemic threat.
Phase 3
An animal or human-animal influenza
reassortant virus has caused sporadic cases or small clusters of disease
in people, but has not resulted in human-to-human transmission
sufficient to sustain community-level outbreaks.
Phase 4
Human to human transmission of an animal or
human-animal influenza reassortant virus able to sustain community-level
outbreaks has been verified.
Phase 5
Human-to-human spread of the virus in two or more countries in one WHO region.
Phase 6
In addition to the criteria defined in Phase
5, the same virus spreads from human-to-human in at least one other
country in another WHO region.
Post peak period
Levels of pandemic influenza in most countries with adequate surveillance have dropped below peak levels.
Post pandemic period
Levels of influenza activity have returned
to the levels seen for seasonal influenza in most countries with
adequate surveillance.
The World Health Organization (WHO) developed a global influenza
preparedness plan, which defines the stages of a pandemic, outlines
WHO's role and makes recommendations for national measures before and
during a pandemic.
In the 2009 revision of the phase descriptions, the WHO has retained the use of a six-phase approach for easy incorporation of new recommendations and approaches into existing national preparedness and response plans.
The grouping and description of pandemic phases have been revised to
make them easier to understand, more precise, and based upon observable
phenomena. Phases 1–3 correlate with preparedness, including capacity
development and response planning activities, while phases 4–6 clearly
signal the need for response and mitigation efforts. Furthermore,
periods after the first pandemic wave are elaborated to facilitate post
pandemic recovery activities.
In February 2020, WHO spokesperson Tarik Jasarevic explained that
the WHO no longer uses this six-phase classification model: "For the
sake of clarification, WHO does not use the old system of 6 phases—that
ranged from phase 1 (no reports of animal influenza causing human
infections) to phase 6 (a pandemic)—that some people may be familiar
with from H1N1 in 2009."
For reference, the phases are defined below.
In nature, influenza viruses circulate continuously among
animals, especially birds. Even though such viruses might theoretically
develop into pandemic viruses, in Phase 1 no viruses circulating among animals have been reported to cause infections in humans.
In Phase 2 an animal influenza virus circulating among
domesticated or wild animals is known to have caused infection in
humans, and is therefore considered a potential pandemic threat.
In Phase 3, an animal or human-animal influenza
reassortant virus has caused sporadic cases or small clusters of disease
in people, but has not resulted in human-to-human transmission
sufficient to sustain community-level outbreaks. Limited human-to-human
transmission may occur under some circumstances, for example, when there
is close contact between an infected person and an unprotected
caregiver. However, limited transmission under such restricted
circumstances does not indicate that the virus has gained the level of
transmissibility among humans necessary to cause a pandemic.
Phase 4 is characterized by verified human-to-human
transmission of an animal or human-animal influenza reassortant virus
able to cause "community-level outbreaks". The ability to cause
sustained disease outbreaks in a community marks a significant upwards
shift in the risk for a pandemic. Any country that suspects or has
verified such an event should urgently consult with the WHO so that the
situation can be jointly assessed and a decision made by the affected
country if implementation of a rapid pandemic containment operation is
warranted. Phase 4 indicates a significant increase in risk of a
pandemic but does not necessarily mean that a pandemic is a foregone
conclusion.
Phase 5 is characterized by human-to-human spread of the
virus into at least two countries in one WHO region. While most
countries will not be affected at this stage, the declaration of Phase 5
is a strong signal that a pandemic is imminent and that the time to
finalize the organization, communication, and implementation of the
planned mitigation measures is short.
Phase 6, the pandemic phase, is characterized by community
level outbreaks in at least one other country in a different WHO region
in addition to the criteria defined in Phase 5. Designation of this
phase will indicate that a pandemic is under way.
During the post-peak period, pandemic disease levels in
most countries with adequate surveillance will have dropped below peak
observed levels. The post-peak period signifies that pandemic activity
appears to be decreasing; however, it is uncertain if additional waves
will occur and countries will need to be prepared for a second wave.
Previous pandemics have been characterized by waves of activity
spread over months. Once the level of disease activity drops, a critical
communications task will be to balance this information with the
possibility of another wave. Pandemic waves can be separated by months
and an immediate "at-ease" signal may be premature.
In the post-pandemic period, influenza disease activity
will have returned to levels normally seen for seasonal influenza. It is
expected that the pandemic virus will behave as a seasonal influenza A
virus. At this stage, it is important to maintain surveillance and
update pandemic preparedness and response plans accordingly. An
intensive phase of recovery and evaluation may be required.
Influenza intervals in the CDC's Pandemic Intervals Framework
In 2014, The United States Centers for Disease Control and Prevention introduced an analogous framework to the WHO's pandemic stages titled the Pandemic Intervals Framework. It includes two pre-pandemic intervals,
Investigation
Recognition
and four pandemic intervals,
Initiation
Acceleration
Deceleration
Preparation
It also includes a table defining the intervals and mapping them to the WHO pandemic stages.
Estimates
of hypothetical influenza deaths in the 2010 United States population
(308,745,538 persons) across varying values of case-fatality ratio and
the cumulative incidence of infection in the population. Selected
estimated numbers of deaths are indicated with a black line, across each
relevant combination of case-fatality ratio and cumulative incidence.
In addition, the background color transitions from blue to yellow to red
as the estimated absolute number of deaths increases. Case-fatality
ratio is an example of a clinical severity measure and cumulative
incidence of infection is an example of a transmissibility measure in
the Pandemic Severity Assessment Framework.
Scaled
examples of past influenza pandemics and past influenza seasons. Color
scheme included to represent corresponding hypothetical estimates of
influenza deaths in the 2010 US population, with the same color scale as
the previous figure.
Historically, measures of pandemic severity were based on the case fatality rate. However, the case fatality rate might not be an adequate measure of pandemic severity during a pandemic response because:
Deaths may lag several weeks behind cases, making the case fatality rate an underestimate
The total number of cases may not be known, making the case fatality rate an overestimate
A single case fatality rate for the entire population may obscure
the effect on vulnerable sub-populations, such as children, the elderly,
those with chronic conditions, and members of certain racial and ethnic
minorities
Fatalities alone may not account for the full effects of the pandemic, such as absenteeism or demand on healthcare services
To account for the limitations of measuring the case fatality rate
alone, the PSAF rates severity of a disease outbreak on two dimensions:
clinical severity of illness in infected persons; and the
transmissibility of the infection in the population. Each dimension can be measured using more than one measure, which are scaled to allow comparison of the different measures.
If influenza remains an animal problem with limited
human-to-human transmission it is not a pandemic, though it continues to
pose a risk. To prevent the situation from progressing to a pandemic,
the following short-term strategies have been put forward:
The rationale for vaccinating poultry workers against common flu is
that it reduces the probability of common influenza virus recombining
with avian H5N1 virus to form a pandemic strain. Longer-term strategies
proposed for regions where highly pathogenic H5N1 is endemic in wild
birds have included:
changing local farming practices to increase farm hygiene and reduce contact between livestock and wild birds.
altering farming practices in regions where animals live in close,
often unsanitary quarters with people, and changing the practices of
open-air "wet markets"
where birds are kept for live sale and slaughtered on-site. A challenge
to implementing these measures is widespread poverty, frequently in
rural areas, coupled with a reliance upon raising fowl for purposes of subsistence farming or income without measures to prevent propagation of the disease.
changing local shopping practices from purchase of live fowl to purchase of slaughtered, pre-packaged fowl.
improving veterinary vaccine availability and cost.
The
main ways available to tackle a flu pandemic initially are behavioural.
Doing so requires a good public health communication strategy and the
ability to track public concerns, attitudes and behaviour. For example,
the Flu TElephone Survey Template (FluTEST) was developed for the UK
Department of Health as a set of questions for use in national surveys
during a flu pandemic.
Social distancing: By traveling less, working from home
or closing schools, there is less opportunity for the virus to spread.
Reduce the time spent in crowded settings if possible. And keep your
distance (preferably at least 1 metre) from people who show symptoms of
influenza-like illness, such as coughing and sneezing.
However, social distancing during a pandemic flu will likely carry
severe mental health consequences; therefore, sequestration protocols
should take mental health issues into consideration.
Respiratory hygiene: Advise people to cover their coughs and
sneezes. If using a tissue, make sure you dispose of it carefully and
then clean your hands immediately afterwards. (See "Handwashing Hygiene"
below.) If you do not have a tissue handy when you cough or sneeze,
cover your mouth as much as possible with the crook of your elbow.
Handwashing hygiene: Frequent handwashing with soap and water
(or with an alcohol-based hand sanitizer) is very important, especially
after coughing or sneezing, and after contact with other people or with
potentially contaminated surfaces (such as handrails, shared utensils,
etc.)
Other hygiene: Avoid touching your eyes, nose and mouth as much as possible.
Masks: No mask can provide a perfect barrier, but products that meet or exceed the NIOSH N95 standard recommended by the World Health Organization are thought to provide good protection. WHO recommends that health-care workers wear N95 masks and that patients wear surgical masks (which may prevent respiratory secretions from becoming airborne).
Any mask may be useful to remind the wearer not to touch the face. This
can reduce infection due to contact with contaminated surfaces,
especially in crowded public places where coughing or sneezing people
have no way of washing their hands. The mask itself can become
contaminated and must be handled as medical waste when removed.
Risk communication:
To encourage the public to comply with strategies to reduce the spread
of disease, "communications regarding possible community interventions
[such as requiring sick people to stay home from work, closing schools]
for pandemic influenza that flow from the federal government to
communities and from community leaders to the public not overstate the
level of confidence or certainty in the effectiveness of these
measures."
The Institute of Medicine
has published a number of reports and summaries of workshops on public
policy issues related to influenza pandemics. They are collected in Pandemic Influenza: A Guide to Recent Institute of Medicine Studies and Workshops, and some strategies from these reports are included in the list above. Relevant learning from the 2009 flu pandemic in the UK was published in Health Technology Assessment, volume 14, issue 34. Asymptomatic transmission appears to play a small role, but was not well studied by 2009.
Anti-viral drugs
There
are two groups of antiviral drugs available for the treatment and
prophylaxis of influenza: neuraminidase inhibitors such as Oseltamivir (trade name Tamiflu) and Zanamivir
(trade name Relenza), and adamantanes such as amantadine and
rimantadine. Due to the high rate of side effects and risk of antiviral
resistance, use of adamantanes to fight influenza is limited.
Many nations, as well as the World Health Organization, are working to stockpile anti-viral drugs in preparation for a possible pandemic. Oseltamivir is the most commonly sought drug, since it is available in pill form. Zanamivir
is also considered for use, but it must be inhaled. Other anti-viral
drugs are less likely to be effective against pandemic influenza.
Both Tamiflu and Relenza are in short supply, and production
capabilities are limited in the medium term. Some doctors say that
co-administration of Tamiflu with probenecid could double supplies.
There also is the potential of viruses to evolve drug resistance.
Some H5N1-infected persons treated with oseltamivir have developed
resistant strains of that virus.
Vaccines
A vaccine probably would not be available in the initial stages of population infection.
A vaccine cannot be developed to protect against a virus which does not
exist yet. The avian flu virus H5N1 has the potential to mutate into a
pandemic strain, but so do other types of flu virus. Once a potential
virus is identified and a vaccine is approved, it normally takes five to
six months before the vaccine becomes available.
The capability to produce vaccines varies widely from country to
country; only 19 countries are listed as "influenza vaccine
manufacturers" according to the World Health Organization.
It is estimated that, in a best scenario situation, 750 million doses
could be produced each year, whereas it is likely that each individual
would need two doses of the vaccine to become immuno-competent.
Distribution to and inside countries would probably be problematic.
Several countries, however, have well-developed plans for producing
large quantities of vaccine. For example, Canadian health authorities
say that they are developing the capacity to produce 32 million doses
within four months, enough vaccine to inoculate every person in the
country.
Another concern is whether countries which do not manufacture
vaccines themselves, including those where a pandemic strain is likely
to originate, will be able to purchase vaccine to protect their
population. Cost considerations aside, they fear that the countries with
vaccine-manufacturing capability will reserve production to protect
their own populations and not release vaccines to other countries until
their own population is protected. Indonesia has refused to share
samples of H5N1 strains which have infected and killed its citizens
until it receives assurances that it will have access to vaccines
produced with those samples. So far, it has not received those
assurances.
However, in September 2009, Australia, Brazil, France, Italy, New
Zealand, Norway, Switzerland, the UK, and the USA agreed to make 10
percent of their H1N1 vaccine supply available to less-developed
countries.
There are two serious technical problems associated with the
development of a vaccine against H5N1. The first problem is this:
seasonal influenza vaccines require a single injection of 15 μg
haemagluttinin in order to give protection; H5 seems to evoke only a
weak immune response and a large multicentre trial found that two
injections of 90 µg H5 given 28 days apart provided protection in only
54% of people.
Even if it is considered that 54% is an acceptable level of protection,
the world is currently capable of producing only 900 million doses at a
strength of 15 μg (assuming that all production were immediately
converted to manufacturing H5 vaccine); if two injections of 90 μg are
needed then this capacity drops to only 70 million. Trials using adjuvants such as alum, AS03, AS04 or MF59 to try and lower the dose of vaccine are urgently needed. The second problem is this: there are two circulating clades
of virus, clade 1 is the virus originally isolated in Vietnam, clade 2
is the virus isolated in Indonesia. Vaccine research has mostly been
focused on clade 1 viruses, but the clade 2 virus is antigenically
distinct and a clade 1 vaccine will probably not protect against a
pandemic caused by clade 2 virus.
Since 2009, most vaccine development efforts have been focused on
the current pandemic influenza virus H1N1. As of July 2009, more than
70 known clinical trials have been completed or are ongoing for pandemic
influenza vaccines.
In September 2009, the US Food and Drug Administration approved four
vaccines against the 2009 H1N1 influenza virus, and expected the initial
vaccine lots to be available within the following month.
Government preparations for a potential H5N1 pandemic (2003–2009)
According to The New York Times
as of March 2006, "governments worldwide have spent billions planning
for a potential influenza pandemic: buying medicines, running disaster
drills, [and] developing strategies for tighter border controls" due to
the H5N1 threat.
[T]he United States is collaborating closely with eight international organizations, including the World Health Organization (WHO), the Food and Agriculture Organization of the United Nations (FAO), the World Organization for Animal Health
(OIE), and 88 foreign governments to address the situation through
planning, greater monitoring, and full transparency in reporting and
investigating avian influenza occurrences. The United States and these
international partners have led global efforts to encourage countries to
heighten surveillance for outbreaks in poultry and significant numbers
of deaths in migratory birds and to rapidly introduce containment
measures. The U.S. Agency for International Development (USAID) and the U.S. Departments of State, Health and Human Services (HHS), and Agriculture
(USDA) are coordinating future international response measures on
behalf of the White House with departments and agencies across the
federal government.
Together steps are being taken to "minimize the risk of further
spread in animal populations", "reduce the risk of human infections",
and "further support pandemic planning and preparedness".
In September 2005, David Nabarro,
a lead UN health official, warned that a bird flu outbreak could happen
at any time and had the potential to kill 5–150 million people.
World Health Organization
The World Health Organization
(WHO), believing that the world was closer to another influenza
pandemic than it has been any time since 1968, when the last of the 20th
century's three pandemics
swept the globe, has developed guidelines on pandemic influenza
preparedness and response. The March 2005 plan includes guidance on
roles and responsibilities in preparedness and response; information on
pandemic phases; and recommended actions for before, during, and after a
pandemic.
United States
"[E]fforts
by the federal government to prepare for pandemic influenza at the
national level include a $100 million DHHS initiative in 2003 to build
U.S. vaccine production. Several agencies within Department of Health and Human Services (DHHS)—including the Office of the Secretary, the Food and Drug Administration (FDA), CDC, and the National Institute of Allergy and Infectious Diseases
(NIAID)—are in the process of working with vaccine manufacturers to
facilitate production of pilot vaccine lots for both H5N1 and H9N2
strains as well as contracting for the manufacturing of 2 million doses
of an H5N1 vaccine. This H5N1 vaccine production will provide a critical
pilot test of the pandemic vaccine system; it will also be used for
clinical trials to evaluate dose and immunogenicity and can provide
initial vaccine for early use in the event of an emerging pandemic."
Each state and territory of the United States has a specific
pandemic flu plan which covers avian flu, swine flu (H1N1), and other
potential influenza epidemics. The state plans together with a
professionally vetted search engine of flu related research, policies,
and plans, is available at the current portal: Pandemic Flu Search.
On 26 August 2004, Secretary of Health and Human Services, Tommy Thompson released a draft Pandemic Influenza Response and Preparedness Plan,
which outlined a coordinated national strategy to prepare for and
respond to an influenza pandemic. Public comments were accepted for 60
days.
On 27 October 2005, the Department of Health and Human Services awarded a $62.5 million contract to Chiron Corporation
to manufacture an avian influenza vaccine designed to protect against
the H5N1 influenza virus strain. This followed a previous awarded
$100 million contract to sanofi pasteur, the vaccines business of the sanofi-aventis Group, for avian flu vaccine.
In October 2005, Bush urged bird flu vaccine manufacturers to increase their production.
On 1 November 2005 Bush unveiled the National Strategy To Safeguard Against The Danger of Pandemic Influenza.
He also submitted a request to Congress for $7.1 billion to begin
implementing the plan. The request includes $251 million to detect and
contain outbreaks before they spread around the world; $2.8 billion to
accelerate development of cell-culture technology; $800 million for
development of new treatments and vaccines; $1.519 billion for the
Departments of Health and Human Services (HHS)
and Defense to purchase influenza vaccines; $1.029 billion to stockpile
antiviral medications; and $644 million to ensure that all levels of
government are prepared to respond to a pandemic outbreak.
On 6 March 2006, Mike Leavitt,
Secretary of Health and Human Services, said U.S. health agencies are
continuing to develop vaccine alternatives that will protect against the
evolving avian influenza virus.
The U.S. government, bracing for the possibility that migrating
birds could carry a deadly strain of bird flu to North America, plans to
test nearly eight times as many wild birds starting in April 2006 as
have been tested in the past decade.
On 8 March 2006, Dr. David Nabarro,
senior UN coordinator for avian and human influenza, said that given
the flight patterns of wild birds that have been spreading avian
influenza (bird flu) from Asia to Europe and Africa, birds infected with
the H5N1 virus could reach the Americas within the next six to 12
months.
July 5, 2006, (CIDRAP
News) – "In an update on pandemic influenza preparedness efforts, the
federal government said last week it had stockpiled enough vaccine
against H5N1 avian influenza virus to inoculate about 4 million people
and enough antiviral medication to treat about 6.3 million."
Canada
The Public Health Agency of Canada follows the WHO's categories, but has expanded them.
The avian flu scare of 2006 prompted The Canadian Public Health Agency
to release an updated Pandemic Influenza Plan for Health Officials. This
document was created to address the growing concern over the hazards
faced by public health officials when exposed to sick or dying patients.
Malaysia
Since the Nipah virus outbreak in 1999, the Malaysian Health Ministry
have put in place processes to be better prepared to protect the
Malaysian population from the threat of infectious diseases. Malaysia
was fully prepared during the Severe Acute Respiratory Syndrome (SARS) situation (Malaysia was not a SARS-affected country) and the episode of the H5N1 (bird flu) outbreak in 2004.
The Malaysian government has developed a National Influenza Pandemic Preparedness Plan (NIPPP)
which serves as a time bound guide for preparedness and response plan
for influenza pandemic. It provides a policy and strategic framework for
a multisectoral response and contains specific advice and actions to be
undertaken by the Ministry of Health at the different levels, other
governmental departments and agencies and non-governmental organizations
to ensure that resources are mobilized and used most efficiently
before, during and after a pandemic episode.
