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Swine Flu (cont.)

The 2009 and 2011 Outbreaks of Swine Influenza

In March and April 2009, hundreds of cases of human respiratory illness were reported in Mexico that were suspected or confirmed to be caused by a novel swine-type influenza virus. By April, confirmed cases were also reported in the United States. The first reported cases in the U.S. came from San Diego County and Imperial County in California and Guadalupe County in Texas. Reports from other states rapidly followed, and the disease spread rapidly around the globe. The World Health Organization (WHO) officially declared the 2009 swine flu to be a pandemic. The U.S. Centers for Disease Control and Prevention (CDC) estimated that more than 1 million Americans were infected with swine influenza by June 2009. By August 2009, more than 170 countries and territories reported swine flu cases. By October, 46 U.S. states were reporting widespread outbreaks. By late October, the virus had been confirmed to have caused more than 1,000 deaths in the U.S., with almost 100 of the deaths in children. Approximately 6% of deaths were in pregnant women, although only 1% of the population was pregnant. Physician visits, hospitalizations, and deaths in the fall of 2009 all exceeded seasonal thresholds. On Oct. 25, 2009, President Obama declared a national emergency as a result of the outbreak. This allowed public-health officials additional power to allow waive some regulations to facilitate patient care and allowed hospitals to set up separate facilities to isolate sick patients.

A new vaccine was emergently made against H1N1 virus, and while during the first several months of the pandemic it was in short supply, it eventually became available worldwide. As the H1N1 pandemic began to wane, the statistics suggested that the H1N1 infections more closely resembled a potent seasonal flu outbreak. However, a H1N1 virus strain has been included in the all of the seasonal trivalent vaccines since the 2011-2012 flu season.

In 2011, the CDC reported a new assortment of genetic material from H1N1 and H3N2 influenza A viruses that resulted in a new strain of swine virus termed influenza A (H3N2)v (also termed H3N2v) that was similar to viruses that infected pigs in the 1990s. However, this strain genetically picked up an M gene from H1N1 that researchers suggest allowed the viral strain to more easily infect humans. In the fall of 2011, the CDC reported that about 12 confirmed human infections were detected in young people who often had some association with pigs or pig farming. In July 2012, the CDC noted a rapid rise in these H3N2v infections that again occurred with people associated with pigs and pig farming. In addition, a new virus with the same H and N designations but antigenically different from H3N2v also caused flu; it is designated as H3N2. This outbreak also was noted in 2011 and infected many people worldwide but was not a pandemic. The newest seasonal flu shots and nasal spray vaccines now contain H3N2 antigens to offer protection against the H2N2 flu virus, but the resultant vaccine is not effective against H3N2v.

Medically Reviewed by a Doctor on 6/24/2015

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