2009 swine flu outbreak A/H1N1 virus

The 2009 swine flu outbreak is an epidemic of a new strain of Influenza A virus subtype H1N1 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).^[59] A June 10th update by the U.N.'s World Health Organization (WHO) states that "74 countries have officially reported 27,737 cases of influenza A(H1N1) infection, including 141 deaths."^[60]

The outbreak began in Mexico, where early reports indicated a surge of cases that had already killed at least 81 people by April 26. As a result, WHO and 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 flu pandemic is "imminent". Most cases throughout the world have so far been mild relative to seasonal flu.^[61] But because this is a new virus, most people do not have immunity to it, and illness may eventually become more severe and widespread in different demographic and population groups. This new H1N1 flu mainly spreads in humans 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 properly cooked pork.^[62]

There was no vaccine available to prevent infection as of June 2009^[update], although companies were developing one and estimates of availability ranged from three to six months. There is also concern that the virus could mutate over the coming months to a more dangerous flu outbreak later in the year, and a vaccine produced now might be less effective in preventing its spread. Health officials in the U.S. pointed out that the "terrible experience" of the 1918 flu pandemic, which killed approximately 600,000 in the United States alone, was preceded by a mild "herald" wave of cases in the spring.^[63]

By early June, most of the deaths from the illness had taken place in Mexico. This led to speculation that Mexico may have been in the midst of an unrecognized epidemic for months prior to the current outbreak, thereby showing a fatality rate that was much higher than it would have been if earlier cases had been counted. According to the CDC, the fact that the flu's infection activity is now monitored more closely may also help explain why more flu cases than normal are being recorded in many countries.^[63]