A pandemic ends, but there may be an H1N1 encore

The H1N1 (swine) flu virus that emerged in Mexico and California in 2009 and quickly spread across the globe was downgraded from a pandemic by the World Health Organization this week. "The public health emergency of international concern, recommended following the emergence of the H1N1 (2009) virus, should be considered over," says the WHO after looking at international epidemiological data. The 2009 H1N1 flu is still active around the world, but is behaving more like a seasonal form of influenza, according to WHO scientists.

In June of last year, the WHO declared H1N1 a phase six pandemic flu because most people had little or no immunity, and it had reached sustained person-to-person transmission in multiple parts of the world. Today, according to statement by WHO director-general Margaret Chan M.D., some areas have seen infection rates of 20 to 40 percent, and many countries report good vaccination rates, both of which contribute to community-wide immunity. And many older adults, as was found last year, seem to have some preexisting immunity from a similar virus long ago.

That doesn't mean the end of the H1N1 flu itself. The full extent of the flu that many feared after the initial reports of deaths in Mexico City last spring thankfully never materialized. But the H1N1 flu did cause deaths and severe disease in young children, pregnant women, people with chronic health conditions, and even healthy adults and children worldwide. As the H1N1 flu shifts to a seasonal pattern, there may be fewer infections overall, but those infections can still be serious. The WHO and the Centers for Disease Control and Prevention still recommend the H1N1 flu vaccine for those with certain risk factors, until the seasonal vaccine is available this fall. The 2010 seasonal vaccine will protect against the H1N1 flu, as well as other strains expected to circulate this flu season.
 
—Kevin McCarthy, associate editor

—Aaron Bailey