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It's official: You survived the pandemic
WHO scales down response, advises vigilance
Like a hurricane downgraded to a tropical depression, H1N1 influenza A has lost its pandemic status and is now just another troublesome flu bug as infection preventionists prepare for the annual outbreak season.
The World Health Organization recently made it official, basing its assessment on the global situation, as well as reports from several countries that are now experiencing influenza.
"As we enter the post-pandemic period, this does not mean that the H1N1 virus has gone away," says Margaret Chan, MD, director general of the WHO in Geneva. "Based on experience with past pandemics, we expect the H1N1 virus to take on the behavior of a seasonal influenza virus and continue to circulate for some years to come."
In the post-pandemic period, localized outbreaks of different magnitude may show significant levels of H1N1 transmission. "This is the situation we are observing right now in New Zealand, and may see elsewhere," she says. "In fact, the actions of health authorities in New Zealand, and also in India, in terms of vigilance, quick detection and treatment, and recommended vaccination, provide a model of how other countries may need to respond in the immediate post-pandemic period."
Globally, the levels and patterns of H1N1 transmission now being seen differ significantly from what was observed during the pandemic, Chan says. Out-of-season outbreaks are no longer being reported in either the northern or southern hemisphere. Influenza outbreaks, including those primarily caused by the H1N1 virus, show an intensity similar to that seen during seasonal epidemics.
"During the pandemic, the H1N1 virus crowded out other influenza viruses to become the dominant virus," Chan says. "This is no longer the case. Many countries are reporting a mix of influenza viruses, again as is typically seen during seasonal epidemics."
Recently published studies indicate that 20–40% of populations in some areas have been infected by the H1N1 virus and thus have some level of protective immunity. Many countries report good vaccination coverage, especially in high-risk groups, and this coverage further increases community-wide immunity, Chan reported.
"Based on available evidence and experience from past pandemics, it is likely that the virus will continue to cause serious disease in younger age groups, at least in the immediate post-pandemic period," she warned. "Groups identified during the pandemic as at higher risk of severe or fatal illness will probably remain at heightened risk, though hopefully the number of such cases will diminish."
In addition, a small proportion of people infected during the pandemic, including young and healthy people, developed a severe form of primary viral pneumonia that is not typically seen during seasonal epidemics and is especially difficult and demanding to treat. It is not known whether this pattern will change during the post-pandemic period, further emphasizing the need for vigilance, Chan noted.