United States

The new strain was first diagnosed in two children, neither of whom had been in contact with pigs, by the CDC, first on April 14, 2009 in San Diego County, California and a few days later in nearby Imperial County, California[27] (it was not identified as a new strain in Mexico until 24 April

Response

The Public Health Agency of Canada announced that their National Microbiology Laboratory (NML) had mapped the genetic code of the swine flu virus, the first time that was done.[29]

U.S officials noted that six years of worrying about H5N1 avian flu did much to prepare for the current swine flu outbreak, noting that after H5N1 emerged in Asia, ultimately killing about 60 percent of the few hundred people infected by it over the years, many countries took steps to try to prevent any similar crisis from spreading further.[30][31] The CDC would now use the current lull to take stock of the United States's response to the new H1N1 flu and attempt to patch any gaps in the public health safety net before flu season starts this autumn.

Pigs and food safety

The novel H1N1 virus is a type of swine influenza, derived originally from a strain that lived in pigs and this origin gave rise to the common name of "swine flu", largely used today by mass media. Despite this origin, however, the current strain is transmitted between people and not from swine.[33] The U.S. agriculture secretary has made it clear that despite its common name, "swine flu," there is no risk in eating cooked pork products and the virus has not been found in American hogs

Initial outbreaks

It is not known where the virus originated.[20][21] 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 identified as being due to a new strain.

Mexico

The virus was first reported in two U.S. children in March, but health officials have said that it apparently infected people as early as last January in Mexico.[24] The outbreak was first detected in Mexico City on March 18, 2009,[25] Immediately after the outbreak was officially announced, Mexico requested material support from the U.S., and within days of the outbreak Mexico City was "effectively shut down." Some countries canceled flights to Mexico while others halted trade. Calls to close the border to contain the spread were rejected.

Some experts today assume that Mexico already had hundreds of thousands, and possibly millions, of cases before the outbreak was officially recognized, and was therefore in the midst of a "silent epidemic".[26] As a result, Mexico was reporting only the most serious cases, possibly leading to a skewed initial estimate of the case fatality rate.

Historical context

Annual influenza epidemics are estimated to affect 5–15% of the global population. Although most cases are mild, this still causes severe illness in 3–5 million people and around 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.[7]

In addition to these annual epidemics, Influenza A virus strains caused three major global epidemics 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 strains of Influenza A virus that had undergone major genetic changes and for which the population did not possess significant immunity.[7][8] The overall effects of these pandemics and epidemics are summarized in the table below.

Historical context 2

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.[8] The world has been at an increased level of alert since the SARS epidemic in Southeast Asia (caused by the SARS coronavirus).[16] 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.[9][17]

People who have contracted flu prior to 1957 may have some immunity. A May 20, 2009 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