This article covers the chronology of the 2009 novel influenza A (H1N1) pandemic. Flag icons denote the first announcements of confirmed cases by the respective nation-states, their first deaths (and other major events such as their first intergenerational cases, cases of zoonosis, and the start of national vaccination campaigns), and relevant sessions and announcements of the World Health Organization (WHO), the European Union (and its agency the European Centre for Disease Prevention and Control), and the U.S. Centers for Disease Control (CDC).
Unless otherwise noted, references to terms like S-OIV, H1N1 and such, all refer to this new A(H1N1) strain and not to sundry other strains of H1N1 which are endemic in humans, birds and pigs.
2009 | A(H1N1) Outbreak and Pandemic Milestones |
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17 June | ![]() |
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18 June | ![]() |
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30 June | ![]() |
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1 July | ![]() |
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26 July | ![]() |
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2 August | ![]() |
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11 September | ![]() |
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1 October | ![]() |
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13 October | ![]() |
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29 October | ![]() |
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30 October | ![]() |
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1 November | ![]() |
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2010 | A(H1N1) Outbreak and Pandemic Milestones |
1 January | ![]() |
5 January | ![]() |
11 January | ![]() |
15 January | ![]() |
19 January | ![]() |
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29 January | ![]() |
3 February | ![]() |
9 February | ![]() |
25 February | ![]() |
27 March | ![]() |
2 April | ![]() |
12 April | ![]() |
26 April | ![]() |
10 August | ![]() |
Influenza A virus (IAV) is a pathogen with strains that infect birds and some mammals, as well as causing seasonal flu in humans. Mammals in which different strains of IAV circulate with sustained transmission are bats, pigs, horses and dogs; other mammals can occasionally become infected.
Swine influenza is an infection caused by any of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) refers to any strain of the influenza family of viruses that is endemic in pigs. As of 2009, identified SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H2N1, H3N1, H3N2, and H2N3.
In virology, influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus. Major outbreaks of H1N1 strains in humans include the 1918 Spanish flu pandemic, the 1977 Russian flu pandemic and the 2009 swine flu pandemic. It is an orthomyxovirus that contains the glycoproteins hemagglutinin (H) and neuraminidase (N), antigens whose subtypes are used to classify the strains of the virus as H1N1, H1N2 etc. Hemagglutinin causes red blood cells to clump together and binds the virus to the infected cell. Neuraminidase is a type of glycoside hydrolase enzyme which helps to move the virus particles through the infected cell and assist in budding from the host cells.
An influenza pandemic is an epidemic of an influenza virus that spreads across a large region 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 2009 swine flu pandemic resulted in under 300,000 deaths and is considered relatively mild. These pandemics occur irregularly.
Influenza, commonly known as "the flu" or just "flu", is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin one to four days after exposure to the virus and last for about two to eight days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia from the virus or a subsequent bacterial infection. Other complications include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease.
The 2009 swine flu pandemic, caused by the H1N1/swine flu/influenza virus and declared by the World Health Organization (WHO) from June 2009 to August 2010, was the third recent flu pandemic involving the H1N1 virus. The first identified human case was in La Gloria, Mexico, a rural town in Veracruz. The virus appeared to be a new strain of H1N1 that resulted from a previous triple reassortment of bird, swine, and human flu viruses which further combined with a Eurasian pig flu virus, leading to the term "swine flu".
The 2009 flu pandemic in the United States was caused by a novel strain of the Influenza A/H1N1 virus, commonly referred to as "swine flu", that was first detected on 15 April 2009. While the 2009 H1N1 virus strain was commonly referred to as "swine flu", there is no evidence that it is endemic to pigs or of transmission from pigs to people; instead, the virus spreads from person to person. On April 25, the World Health Organization declared a public health emergency, followed concurringly by the Obama administration on April 26.
The 2009 swine flu pandemic in Canada was part of an epidemic in 2009 of a new strain of influenza A virus subtype H1N1 causing what has been commonly called swine flu. In Canada, roughly 10% of the populace has been infected with the virus, with 428 confirmed deaths ; non-fatal individual cases are for the most part no longer being recorded. About 40% of Canadians have been immunized against H1N1 since a national vaccination campaign began in October 2009, with Canada among the countries in the world leading in the percentage of the population that has been vaccinated. The widespread effect of H1N1 in Canada raised concerns during the months leading to the XXI Olympic Winter Games, which took place in Vancouver in February 2010.
This article covers the chronology of the 2009 novel influenza A (H1N1) pandemic. Flag icons denote the first announcements of confirmed cases by the respective nation-states, their first deaths, and relevant sessions and announcements of the World Health Organization (WHO), the European Union , and the U.S. Centers for Disease Control (CDC).
In March and April 2009, an outbreak of a new strain of influenza commonly referred to as "swine flu" infected many people in Mexico and other parts of the world, causing illness ranging from mild to severe. Initial reports suggested that the outbreak had started in February due to farming practices at a pig farm half-owned by Smithfield Foods. Smithfield Foods stated that it had found no clinical signs or symptoms of the presence of swine influenza in the company's swine herd, or among its employees at its joint ventures in Mexico, that it routinely administers influenza virus vaccination to their swine herds and that it conducts monthly testing for the presence of swine influenza. The new strain was identified as a combination of several different strains of Influenzavirus A, subtype H1N1, including separate strains of this subtype circulating in humans and in pigs.
In March and April 2009, an outbreak of a new strain of influenza commonly referred to as swine flu infected many people in Mexico and parts of the United States causing severe illness in the former. The new strain was identified as a combination of several different strains of Influenzavirus A, subtype H1N1, including separate strains of this subtype circulating in humans and in pigs. Spain was the first country in continental Europe to report cases of swine flu, in late April 2009.
The pandemic H1N1/09 virus is a swine origin influenza A virus subtype H1N1 strain that was responsible for the 2009 swine flu pandemic. This strain is often called swine flu by the public media due to the prevailing belief that it originated in pigs. The virus is believed to have originated around September 2008 in central Mexico.
The 2009 Japan flu pandemic was an outbreak of the H1N1 and the Influenza A viruses across Japan. The World Health Organization raised the pandemic alert for influenza to level 4 in April 2009 following a worldwide outbreak of the H1N1 influenza strain. The first Japanese infections of H1N1 and Influenza A were both recorded early in May 2009. In August 2009, the government estimated that the virus strains had infected about 760,000 people. At the height of the pandemic in October 2009, it was estimated that 20% of the Japanese population had been infected and that there were on average more than 20 infected people in each Japanese medical facility. The Ministry of Health, Labor and Welfare reported 198 Deaths as of March 30, 2010. Japan put several measures in place to attempt to control the spread of infection including quarantining air travellers entering Japan who were suspected of having the virus and closing schools in areas of Japan with high numbers of infection. The pandemic ended in August 2010 when the World Health Organization announced that worldwide influenza infection number were back to the seasonal average before the outbreak occurred.
The 2009 swine flu pandemic was confirmed to have spread to the Philippines on May 21, 2009. In the following days, several local cases were reported to be caused by contact with two infected Taiwanese women who attended a wedding ceremony in Zambales.
The 2009 flu pandemic in Asia, part of an epidemic in 2009 of a new strain of influenza A virus subtype H1N1 causing what has been commonly called swine flu, afflicted at least 394,133 people in Asia with 2,137 confirmed deaths: there were 1,035 deaths confirmed in India, 737 deaths in China, 415 deaths in Turkey, 192 deaths in Thailand, and 170 deaths in South Korea. Among the Asian countries, South Korea had the most confirmed cases, followed by China, Hong Kong, and Thailand.
The 2009 swine flu pandemic in North America, part of a pandemic in 2009 of a new strain of influenza A virus subtype H1N1 causing what has been commonly called swine flu, began in the United States or Mexico.
The 2009 swine flu pandemic vaccines were influenza vaccines developed to protect against the pandemic H1N1/09 virus. These vaccines either contained inactivated (killed) influenza virus, or weakened live virus that could not cause influenza. The killed virus was injected, while the live virus was given as a nasal spray. Both these types of vaccine were produced by growing the virus in chicken eggs. Around three billion doses were produced, with delivery in November 2009.
The 2009 swine flu pandemic was a global outbreak of a new strain of influenza A virus subtype H1N1, first identified in April 2009, termed Pandemic H1N1/09 virus by the World Health Organization (WHO) and colloquially called swine flu. The outbreak was first observed in Mexico, and quickly spread globally. On the 11th of June 2009, the WHO declared the outbreak to be a pandemic. The overwhelming majority of patients experience mild symptoms, but some persons are at higher risk of suffering more serious effects; such as those with asthma, diabetes, obesity, heart disease, or those who are pregnant or have a weakened immune system. In the rare severe cases, around 3–5 days after symptoms manifest, the sufferer's condition declines quickly, often to the point respiratory failure. Although Ukraine was not (very) affected at first there was on outbreak of the virus in Western Ukraine in early November 2009 that led to the closing of public buildings and cancellation of meetings for three weeks.
2009 swine flu pandemic in Taiwan began on May 20, 2009, when a non-citizen who had been living in Taiwan returned from the United States via Hong Kong. By the end of September, more than 90% of influenza A detected in the community were Influenza A (H1N1).
The 2017–2018 United States flu season lasted from late 2017 through early 2018. The predominant strain of influenza was H3N2. During the spring months of March–May, influenza B virus became dominant.