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H1N1 (swine flu) outbreak


The 2009 outbreak of Influenza A virus subtype H1N1 is an epidemic of a new strain of influenza virus identified in April 2009, commonly referred to as "swine flu." 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 source of the outbreak in humans is still unknown, but cases were first discovered in the U.S. and soon after in Mexico, which had a surge of cases, many of them fatal. As a result, the U.N.'s World Health Organization (WHO), along with the U.S. Centers for Disease Control and Prevention (CDC), expressed concern that this could become a worldwide flu pandemic, with WHO raising its alert level to "Phase 5" out of the six maximum, indicating that a pandemic was "imminent."

According to the CDC, it is not yet clear how serious this new virus actually is compared with other influenza viruses. What is known, they state, is that because this is a new virus, most people will not have immunity to it, and illness may eventually become more severe and widespread in different population groups as a result. The H1N1 flu mainly spreads in the same way that regular "seasonal influenza" spreads, which is through the air from coughs and sneezes or touching those infected. It cannot be transmitted from eating cooked pork and there are no confirmed cases of anyone becoming infected with this new strain by being in contact with pigs.

As yet there is no vaccine available to prevent infection although companies are in the planning stages for having one available later this year. But there is concern that the virus could mutate again over the coming months, leading to a new and potentially more dangerous flu outbreak later in the year, and a vaccine that will be less effective in preventing its spread.

As of May 24, the virus had spread to more than 40 countries; however, nearly 90% of reported deaths have taken place in Mexico. This has led to speculation that Mexico may have been in the midst of an unrecognized epidemic for many months prior to the current outbreak. According to the CDC, the fact that the flu's infection activity is now monitored more closely may help explain why more flu cases than normal are being recorded in Mexico, the United States and other countries. About half of all influenza viruses being detected so far are the new H1N1 virus, which "experts acknowledge is no worse than seasonal influenza for now."

Historical context

Annual influenza epidemics are estimated to affect 5–15% of the global population, resulting in severe illness in 3–5 million patients and causing 250,000–500,000 deaths worldwide. In industrialized countries severe illness and deaths occur mainly in the high-risk populations of infants, the elderly, and chronically ill patients.

In addition to these annual epidemics, the influenza A virus caused three major global pandemics during the 20th century: the Spanish flu in 1918, Asian flu in 1957 and Hong Kong flu in 1968–69. These pandemics were caused by an Influenza A virus that had undergone major genetic changes and for which the population did not possess significant immunity.

The influenza virus has also caused several pandemic threats over the past century, including the pseudo-pandemic of 1947, the 1976 swine flu outbreak and the 1977 Russian flu, all caused by the H1N1 subtype. The world has been at an increased level of alert since the SARS epidemic in Southeast Asia (caused by the SARS coronavirus). The level of preparedness was further increased and sustained with the advent of the H5N1 bird flu outbreaks because of H5N1's high fatality rate, although the strains currently prevalent have limited human-to-human transmission (anthroponotic) capability, or epidemicity.

People who contracted flu prior to 1957 may have some immunity. A May 20th New York Times article stated: “Tests on blood serum from older people showed that they had antibodies that attacked the new virus, Dr. Daniel Jernigan, chief flu epidemiologist at the Centers for Disease Control and Prevention, said in a telephone news conference. That does not mean that everyone over 52 is immune, since some Americans and Mexicans older than that have died of the new flu.

Initial outbreaks


Both the place and the species in which the virus originated are unknown. Analysis has suggested that the H1N1 strain responsible for the current outbreak first evolved around September 2008 and circulated in the human population for several months before the first cases were detected. The new strain was first diagnosed in two children by the CDC, first on April 14 in San Diego County, California and a few days later in nearby Imperial County, California. Neither child had been in contact with pigs.


Further information: 2009 swine flu outbreak in Mexico

The outbreak was first detected in Mexico City, where surveillance began picking up a surge in cases of influenza-like illness starting March 18th. The surge was initially assumed by Mexican authorities to be "late-season flu" outbreak and not a new virus strain. After samples were sent to the CDC in mid-April, however, the Mexican cases were confirmed by the CDC and the World Health Organization to be a new strain of H1N1. Although Mexican news media had speculated that the outbreak may have started at a pig plant that engaged in intensive farming practices, to date, no pigs in Mexico have tested positive for the virus and investigators have found no swine influenza at any of the pig farms.

International cases and media responses

Data accuracy

The initial outbreak received a week of near-constant media attention. Epidemiologists cautioned that the number of cases reported in the early days of an outbreak can be very inaccurate and deceptive due to several causes, among them selection bias, media bias, and incorrect reporting by governments. This could also be due to authorities in different countries looking at different population groups, many poor, which may in part explain higher mortality rates in countries such as Mexico. Furthermore, countries with poor health care systems and older laboratory facilities may take longer to identify or report cases.

Travel advisories

The new strain has spread widely beyond Mexico and the U.S., with confirmed cases in fifty-three countries and suspected cases in fifty-eight. Many countries had earlier advised citizens to avoid traveling to infected areas, especially Mexico, and were monitoring visitors returning from flu-affected areas for possible flu symptoms. In late April Mexico closed all of its schools and public places for a week to control its spread.

Most cases outside North America were recent travellers to Mexico or the U.S. and intra-national infections have been reported only from Mexico, the USA, Canada, the UK, Spain, Germany, Italy, and Belgium.

On May 15th, CDC’s "Travel Health Warning" recommending against non-essential travel to Mexico, in effect since April 27th., was downgraded to a "Travel Health Precaution for Mexico." In lifting its warning, the CDC said, "There is evidence that the Mexican outbreak is slowing down in many cities though not all.” It also said that the “risk of severe disease” from the H1N1 virus "now appears to be less than originally thought."

Government actions against pigs and pork

Although the FAO, WHO, and OIE have reaffirmed that the H1N1 virus is not known to be transmissible from eating cooked pork or pork products,[100] countries including Serbia, China, and Russia, have nevertheless banned the import and sale of pork products "as a precaution against swine flu". And in late April, the Egyptian Government had begun to kill all 300,000 pigs in Egypt, despite a lack of evidence that the pigs had, or were even suspected of having, the virus. This led to clashes between pig owners and the police in Cairo. Egypt's 80-million population consists mainly of Muslims, whose religion forbids them from eating pork, but also has an estimated six to ten percent of its population being native Christians (Copts), who eat pork as part of their diet.

On May 10, in Alberta, Canada, officials quarantined 500 pigs at a pig farm which had caught the H1N1 virus, with evidence that some of the animals may have caught the virus from a person who had recently visited Mexico. Alberta's chief veterinarian says just under 500 hogs have been culled on the pig farm where the new swine flu virus was detected, but not because the animals were sick.

Virus characteristics

The virus is a novel strain of influenza from which human populations have been neither vaccinated nor naturally immunized. The CDC, after examining virus samples from suspected cases in Mexico, matched the strain with those from cases in Texas and California, and found no known linkages to either to animals or one another. It was also determined that the strain contained genes from four different flu viruses: North American swine influenza; North American avian influenza; human influenza; and two swine influenza viruses typically found in Asia and Europe. Further analysis showed that several of the proteins of the virus are most similar to strains that cause mild symptoms in humans, leading some to suggest that the virus is unlikely to cause severe symptoms for most people.

Rate of Infection

According to the World Health Organization, as of May 25, 2009, 53 countries have officially reported 12,515 cases of infection, including 91 deaths.

Recent news reports, however, indicate that the swine flu is spreading more widely than official figures indicate, with outbreaks in Europe and Asia following those of North and South America. According to the CDC, about one in 20 cases is being officially reported in the U.S. In the U.K., according to virologist professor John Oxford, the virus may be 300 times more widespread than health authorities have said, with total infections estimated at 30,000. Oxford's estimate comes as leading scientists are warning that estimates by the U.K. and other governments on the spread of the disease are "meaningless" and hiding its true extent. He also estimates that Japan may have approximately 30,000 cases. Professor Michael Osterholm, one of the world's top flu experts and an adviser to the U.S. government, also called the official figures "meaningless," claiming that officials were not hiding cases, but were not hunting very hard to find them. Oxford also believes that thousands of people have caught the virus and "suffered only the most minor symptoms," or none at all, over the past weeks.

Although the United States is past its flu season, the Southern Hemisphere, where the virus has also spread, is entering the cold months when influenza cases increase. Jeffery Taubenberger, a National Institutes of Health researcher, states that "I am loath to make predictions about what an influenza virus that mutates so rapidly will do," but he believes it will spread across the planet. Other experts concur, adding that "the new swine flu virus is almost certain to eventually infect every continent and country, although that may take years."


Most fatalities in the world have been in Mexico (87%, as of May 24, 2009) where, according to the New York Times, the deaths from the illness have primarily been young, healthy adults. The WHO Rapid Pandemic Assessment Collaboration estimated the case fatality ratio in Mexico prior to mid-April to be 0.4%. This is comparable to that of the 1957 Asian flu, a category 2 pandemic that killed approximately 1 to 4 million people.

By May 17th, the CDC was reporting 4,714 U.S. cases in 47 states resulting in four deaths, but noted that for the most part, the infections continue to be mild -- similar to seasonal flu -- and recovery is fairly quick. Furthermore, analysis hasn't turned up any of the markers which scientists associate with the virulence of the 1918 "Spanish flu" virus, said Nancy Cox, head of the CDC's flu lab.

Majority of fatalities in Mexico

Other early signs from the United States and other countries where the strain is spreading also suggest it is not unusually dangerous, as there have been few deaths outside of Mexico so far. "If that continues to be true," writes the Washington Post, "then it may help explain the mysteriously high mortality in Mexico." The newspaper notes that "it may be that Mexico already has had hundreds of thousands, and possibly millions, of cases -- all but the most serious hidden in the 'noise' of background illness in a crowded population." They speculate that "the fact that most people infected in other countries had recently been to Mexico -- or were in direct contact with someone who had been -- is indirect evidence that the country may have been experiencing a silent epidemic for months." 

"The difference in seriousness between the known U.S. cases and the Mexican cases is the question that everyone wants to answer," notes medical historian and author Maryn McKenna. CNN Health adds that "There are no hard answers, but a consensus is emerging: The disease in Mexico has likely been around longer and infected more people than investigators can confirm." McKenna states that it's possible "there is much more flu in Mexico than we know because it hasn't been counted. That would mean that there are mild cases there as well, but that you have to get to a certain number of cases before, statistically, you start to see the very serious ones, and the U.S. hasn't had that many cases yet."And Louis Sullivan, physician and former head of Health and Human Services under President George H.W. Bush asks, "Do we really know all of the cases that existed in Mexico or is this just the tip of the iceberg?"

Mutation potential

On May 22nd, WHO chief Dr. Margaret Chan said that the virus must be closely monitored in the southern hemisphere, as it could mix with ordinary seasonal influenza and change in unpredictable ways. "In cases where the H1N1 virus is widespread and circulating within the general community, countries must expect to see more cases of severe and fatal infections," she said. "This is a subtle, sneaky virus." 

An international team of researchers who analyzed all eight genes of the new virus confirmed its sneakiness, saying it "was so different from its ancestral strains that it must have been circulating undetected for years." They confirmed it is a hybrid of two other mixtures -- one a so-called triple reassortant of pig, bird and human viruses, and another group of swine viruses from Europe and Asia.

This has led other experts to become concerned that the new virus strain could mutate over the coming months. Guan Yi, a leading virologist from the University of Hong Kong, for instance, has described the new H1N1 influenza virus as "very unstable", meaning it could mix and swap genetic material when exposed to other viruses. During an interview he said "Both H1N1 and H5N1 are unstable so the chances of them exchanging genetic material are higher, whereas a stable (seasonal flu) virus is less likely to take on genetic material." The H5N1 virus is mostly limited to birds, but in rare cases when it infects humans it has a mortality rate of between 60% to 70%. Experts therefore worry about the emergence of a hybrid of the more dangerous H5N1 with the more transmissible H1N1, especially since H5N1 is now believed to be endemic in countries like China, Indonesia, Vietnam and Egypt. The virulence of avian flu is in part due to a nonstructural protein, NS1, which is distinct from its surface antigens and so could potentially be introduced into other flu virus subtypes (subtypes are defined according to their surface antigens - the H and N numbers).

Pandemic potential

The WHO and CDC officials remain concerned that this outbreak may yet become a pandemic. WHO declared a Pandemic Alert Level of five, out of a maximum six, which describes the degree to which the virus has been able to spread among humans, and uses a Pandemic Severity Index, which predicts the number of fatalities if 30% of the human population were infected. By the end of April, however, some scientists believed that this strain was unlikely to cause as many fatalities as earlier pandemics, and may not even be as damaging as a typical flu season. WHO Director General Margaret Chan, on May 22nd, continued to stop short of declaring the outbreak a "pandemic," by moving to alert level six, because of recent doubts fostered by its mild symptoms to date along with fear that a pandemic "declaration would trigger mass panic" and be economically and politically damaging to many countries.

According to some experts, however, the current outbreak is already a pandemic. Michael Osterholm, director of the Center for Infectious Disease Research and Policy of the University of Minneapolis, feels that WHO’s criteria for a pandemic has been met. While Britain’s Health Secretary Alan Johnson has requested that the disease's severity and other determinants, besides its geographic spread, need to be considered before the pandemic alert is raised to the highest of WHO’s 6-level scale, since a move to phase 6 means that "emergency plans are instantly triggered around the globe." In addition, at phase 6, many pharmaceutical companies would switch from making seasonal flu shots to pandemic-specific vaccine, "potentially creating shortages of an immunization to counter the normal winter flu season." Keiji Fukuda, WHO's assistant director general of health security and environment, states that a move to phase 6 would "signify a really substantial increase in risk of harm to people."

Osterholm feels that the primary concern should be "scientific integrity," stating, "If they want to change the definition, then go ahead. But don’t say that we are not in phase 6 right now because we don’t want to go there." Rather than redefine what constitutes a pandemic, he suggests that health officials should help people understand that the current threat may resemble the 1957 or 1968 pandemics, in which fewer than 4 million people died, rather than the 1918 Spanish flu, blamed for killing about 50 million.

Symptoms and expected severity

The signs of infection with swine flu are similar to influenza, and include a fever, coughing, headaches, pain in the muscles or joints, sore throat, chills, fatigue and runny nose. Diarrhea and vomiting have also been reported in some cases. People at higher risk of serious complications include people age 65 years and older, children younger than 5 years old, pregnant women, people of any age with chronic medical conditions (such as asthma, diabetes, or heart disease), and people who are immunosuppressed (e.g., taking immunosuppressive medications or infected with HIV). In children, certain symptoms may require emergency medical attention, including blue lips and skin, dehydration, rapid breathing, excessive sleeping and significant irritability that includes a lack of desire to be held. In adults, shortness of breath, pain in the chest or abdomen, sudden dizziness or confusion may indicate the need for emergency care. In both children and adults, persistent vomiting or the return of flu-like symptoms that include a fever and cough may require medical attention.

There is mounting evidence that the symptoms are so far milder than health officials feared. As of May 21st, for instance, despite 201 confirmed cases in New York City, most have been mild and there has been only one confirmed death from the virus. Similarly, Japan has reported 279, mostly mild flu cases, and no deaths, with their government now reopening schools, stating that the "virus should be considered more like a seasonal flu." In Mexico, where the outbreak began last month, Mexico City officials have lowered their swine flu alert level as no new cases have been reported for a week.

Prevention and treatment

Personal hygiene

Recommendations to prevent infection by the virus consist of the standard personal precautions against influenza. This includes frequent washing of hands with soap and water or with alcohol-based hand sanitizers, especially after being out in public. The CDC advises not touching the mouth, nose or eyes, as these are primary modes of transmission. When coughing, they recommend coughing into a tissue and disposing of the tissue, then immediately washing the hands.  Chance of transmission is also reduced by disinfecting household surfaces, which can be done effectively with a diluted chlorine bleach solution.

Home treatment remedies

The Mayo Clinic has suggested a number of measures to help ease symptoms, including adequate hydration and rest, soup to ease congestion, over-the-counter drugs to relieve pain. The latter will relieve symptoms, but not treat the condition, and runs the risk of overdose or harm to children if used incorrectly. In general, most patients are expected to recover without requiring medical attention, with the exception of individuals with pre-existing or acquired complications.


Sneezing and coughing

There is little data available on the risk of airborne transmission of this particular virus. Mexican authorities have distributed surgical masks to the general public. The UK Health Protection Agency considers facial masks unnecessary for the general public. Many authorities recommend the use of respirators by health-care workers in the vicinity of pandemic flu patients, particularly during aerosol generating procedures (e.g. intubation, chest physiotherapy, bronchoscopy).


Infection can be caused by touching something with flu viruses on it and then touching your mouth or nose. The virus can have a lifetime of up to two hours outside the body, and thus can be transmitted by handling door knobs, glasses, kitchen utensils, or touching the skin of an infected person and then touching your own mouth or eyes.

Pork consumption

The leading international health agencies have stressed that the "influenza viruses are not known to be transmissible to people through eating processed pork or other food products derived from pigs."

Antiviral drugs

According to the CDC, antiviral drugs can be given to treat those who become severely ill, however these antiviral drugs are prescription medicines (pills, liquid or an inhaler) and act against influenza viruses, including H1N1 flu virus. There are two influenza antiviral medications that are recommended for use against H1N1 flu. The drugs that are used for treating H1N1 flu are called oseltamivir (Tamiflu) and zanamivir (Relenza). The CDC notes that as the H1N1 flu spreads, these antiviral drugs may become in short supply. Therefore, the drugs will be given first to those people who have been hospitalized or are at high risk of complications. The drugs work best if given within 2 days of becoming ill, but may be given later if illness is severe or for those at a high risk for complications.

When buying these medications, some agencies such as the MHRA in the UK have recommended not using online sources, as the WHO estimates that half the drugs sold by online pharmacies without a physical address are counterfeit.[140] Medical experts are also concerned that people "racing to grab up antiviral drugs just to feel safe" may eventually lead to the virus developing drug resistance. Partly as a result, experts suggest the medications should be reserved for only the very ill or people with severe immune deficiencies.

In H3N2 strains, Tamiflu treatment leads to resistance in 0.4% of adult cases and 5.5% of children. Resistant strains are usually less transmissible; nonetheless resistant human H1N1 viruses became widely established in previous flu seasons. Marie-Paule Kiely, WHO vaccine research director, has said that it is "almost a given" that the new strain would undergo reassortment with resistant seasonal flu viruses and acquire resistance, but it is not yet known at what level resistance will appear. Simulations suggest that if physicians choose a second effective antiviral such as zanamivir (Relenza) as first-line treatment in even a few percent of cases, this can greatly delay the spread of resistant strains. Even a drug such as amantadine (Symmetrel) for which resistance frequently emerges may be useful in combination therapy.


Influenza vaccines are typically developed to cope with seasonal flu to minimize infection rates, yet it still kills around 500,000 people a year around the world. Currently, most of the world's flu vaccines use an injection of "killed virus," a vaccine method made famous by Jonas Salk when he developed the first vaccine against the polio virus in 1955. As The Economist magazine summarizes the problem today, however, "if a global pandemic is declared and manufacturers are asked to produce a vaccine for H1N1, they are unlikely to be able to respond quickly enough." Furthermore, vaccine producers can produce about a billion doses of any one vaccine each year, so that even if all the capacity was switched to fight the a pandemic flu, as opposed to a seasonal flu, "there would still be a huge global shortfall." Keiji Fukuda of the WHO said, "There’s much greater vaccine capacity than there was a few years ago, but there is not enough vaccine capacity to instantly make vaccines for the entire world’s population for influenza." The seasonal flu vaccine is not believed to protect against the new strain, therefore any existing stock would not be useful.

There is also concern that should a second, deadlier wave of a new H1N1 strain reappear during the Northern autumn of 2009, producing pandemic vaccines now as a precaution may turn out to be a huge waste of resources with serious results, as the vaccine may not be as effective, and there would also be a shortage of seasonal flu vaccine available. William Schaffner, an infectious disease researcher at Vanderbilt University in Tennessee, USA, stated, referring to Northern hemisphere seasons, that "for now, there is no way to tell whether the swine flu will die out this spring, or tarry through the summer and reappear as a stronger, meaner virus in the fall."

The costs of producing a vaccine have also become an issue, with some U.S. lawmakers questioning whether a vaccine is worth the unknown benefits. Representatives Phil Gingrey and Paul Broun, for instance, are not convinced that the U.S. should spend up to $2 billion to produce one, with Gingrey stating "We can’t let all of our spending and our reaction be media-driven in responding to a panic so that we don’t get Katrina-ed. ... It’s important because what we are talking about as we discuss the appropriateness of spending $2 billion to produce a vaccine that may never be used — that is a very important decision that our country has to make."

Moreover, should a pandemic be declared and a vaccine produced, the WHO will attempt to make sure that a substantial amount is available for the benefit of developing countries. Vaccine makers and countries with standing orders, such as the U.S. and a number of European countries, will be asked, according to WHO officials, "to share with developing countries from the moment the first batches are ready if an H1N1 vaccine is made."  The global body stated that it wants companies to donate at least 10 percent of their production or offer reduced prices for poor countries that could otherwise be left without vaccines if there is a sudden surge in demand.

Production decisions

After a meeting with the WHO on May 14, 2009, pharmaceutical companies said they were ready to begin making a swine flu vaccine. According to news reports, the WHO's experts will present recommendations to WHO Director-General Margaret Chan, who is expected to issue advice to vaccine manufacturers and the World Health Assembly next week. WHO's Keiji Fukuda told reporters "These are enormously complicated questions, and they are not something that anyone can make in a single meeting." Most flu vaccine companies can only make one vaccine at a time: seasonal flu vaccine or pandemic vaccine. Production takes months and it is impossible to switch halfway through if health officials make a mistake. . . . if the swine flu mutates, scientists aren't sure how effective a vaccine made now from the current strain will remain." Rather than wait on the WHO decision, however, some countries in Europe have decided to go ahead with early vaccine orders.

A May 20th AP article reported: “Manufacturers won't be able to start making the vaccine until mid-July at the earliest, weeks later than previous predictions, according to an expert panel convened by WHO. It will then take months to produce the vaccine in large quantities. The swine flu virus is not growing very fast in laboratories, making it difficult for scientists to get the key ingredient they need for a vaccine, the "seed stock" from the virus, WHO said. . . . In any case, mass producing a pandemic vaccine would be a gamble, as it would take away manufacturing capacity for the seasonal flu vaccine that kills up to 500,000 people each year. Some experts have wondered whether the world really needs a vaccine for an illness that so far appears mild.” 

Another option proposed by the CDC is an "earlier rollout of seasonal vaccine," according to the CDCs Dr. Daniel Jernigan. He said the CDC would work with vaccine manufacturers and experts to see if that would be possible and desirable. Flu vaccination usually starts in September in the United States and peaks in November. Some vaccine experts agree it would be better to launch a second round of vaccinations against the new H1N1 strain instead of trying to add it to the seasonal flu vaccine or replacing one of its three components with the new H1N1 virus.

As of early May, only a few more weeks were needed for the WHO and CDC to develop a "seed strain" of the pandemic virus, but producers would then need four to six months before they could create large volumes of vaccine. Doris Bucher, who heads one of three labs worldwide tasked with producing seed virus, explained in an interview that her lab produces seed virus using an H3N2 influenza strain, NYMC X-157, which grows quickly in eggs. This strain is allowed to undergo reassortment with the swine flu strain by injecting both at high concentrations into the allantois of an egg so that single cells are infected by both viruses. The resulting hybrid viruses are then subjected to an artificial selection in which any viruses with H3 or N2 antigens are removed, and the strains growing fastest in eggs are favored. The resulting virus resembles swine flu on the outside and X-157 on the inside and can be rapidly grown to produce vaccine. On May 24 the CDC reported that it had created one candidate seed strain and received another from an outside lab. The two strains will be tested there and may be sent out to vaccine manufacturers by the end of May.


On April 28, WHO's Dr. Keiji Fukuda pointed out that it is too late to contain the swine flu. "Containment is not a feasible operation. Countries should now focus on mitigating the effect of the virus," he said. He therefore did not recommend closing borders or restricting travel, stating that "with the virus being widespread... closing borders or restricting travel really has very little effects in stopping the movement of this virus." However, on April 28, the U.S. CDC began "recommending that people avoid non-essential travel to Mexico." Many other countries confirmed that inbound international passengers will be screened. Typical airport health screening involves asking passengers which countries they have visited and checking whether they feel or appear particularly unwell. Thermographic equipment was put into use at a number of airports to screen passengers. A number of countries also advised against travel to known affected regions while experts have suggested that if those infected stay at home or seek medical care, public meeting places are closed, and anti-flu medications are made widely available, then in simulations the sickness is reduced by nearly two-thirds.


Scientific name and common name

According to researchers cited by The New York Times, "based on its genetic structure, the new virus is without question a type of swine influenza, derived originally from a strain that lived in pigs". This origin gave rise to the nomenclature "swine flu", largely used by mass media in the first days of the epidemic. Despite this origin, the current strain is now a human-to-human transmitted virus, requiring no contact with swine. On April 30 the World Health Organization stated that no pigs in any country had been determined to have the illness, but farmers remain alert due to concerns that infected humans may pass the virus to their herds. On May 2, it was announced that a Canadian farm worker who had traveled to Mexico had transmitted the disease to a herd of pigs, showing that the disease can still move between species.

Debate over name

Some authorities object to calling the flu outbreak "swine flu". U.S. Agriculture Secretary Tom Vilsack expressed concerns that this would lead to the misconception that pork is unsafe for consumption. CDC now refers it as Novel influenza A (H1N1). In the Netherlands, it was originally called "pig flu", but is now called "Mexican flu" by the national health institute and in the media. South Korea and Israel briefly considered calling it the "Mexican virus". Currently, the South Korean press uses "SI", short for "swine influenza". Taiwan suggested the names "H1N1 flu" or "new flu", which most local media now use. The World Organization for Animal Health has proposed the name "North American influenza". The European Commission uses the term "novel flu virus".

The WHO announced they would refer to the new influenza virus as Influenza A (H1N1) or "Influenza A (H1N1) virus, human" as opposed to "swine flu", also to avoid suggestions that eating pork products carried a risk of infection.

The outbreak has also been called the "H1N1 influenza", "2009 H1N1 flu", or "swine-origin influenza". However, Seth Borenstein, writing for the Associated Press quoted several experts who objected to any name change at all.


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