WHO Announces H1N1 is in Post-Pandemic Period

Margaret Chan, head of the World Health Organization (WHO) and members of its Emergency Committee, have declared that H1N1 influenza has entered a post-pandemic period. According to Chan, the committee based its assessment on the global situation, as well as reports from several countries that are now experiencing influenza.

Chan states, "As we enter the post-pandemic period, this does not mean that the H1N1 virus has gone away. 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. 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. 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."

Chan continues, "During the pandemic, the H1N1 virus crowded out other influenza viruses to become the dominant virus. 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 percent to 40 percent 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. Pandemics, like the viruses that cause them, are unpredictable. So is the immediate post-pandemic period. There will be many questions, and we will have clear answers for only some. Continued vigilance is extremely important, and WHO has issued advice on recommended surveillance, vaccination, and clinical management during the post-pandemic period."

Based on available evidence and experience from past pandemics, Chan says "it is likely that the virus will continue to cause serious disease in younger age groups, at least in the immediate post-pandemic period. 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 emphasizes pandemics' ability to "deliver surprises." She explains, "No two pandemics are ever alike. This pandemic has turned out to be much more fortunate than what we feared a little over a year ago. This time around, we have been aided by pure good luck. The virus did not mutate during the pandemic to a more lethal form. Widespread resistance to oseltamivir did not develop. The vaccine proved to be a good match with circulating viruses and showed an excellent safety profile. Thanks to extensive preparedness and support from the international community, even countries with very weak health systems were able to detect cases and report them promptly. Had things gone wrong in any of these areas, we would be in a very different situation today."

The Department of Health and Human Services (HHS) has issued a statement regarding implications for the United States:

"This is a formal WHO declaration regarding the end of the pandemic at the global level. The U.S. Public Health Emergency determination for 2009 H1N1 Influenza expired on June 23, 2010. The only impact on the United States resulting from the WHO declaration will be a cessation in weekly reporting under the International Health Regulations (IHR) to the Pan American Health Organization and the World Health Organization. CDC has reported weekly to IHR since early in the pandemic. There are no changes for the United States in terms of CDCs recommendations for the upcoming influenza season and the United States is already proceeding with the understanding that the 2009 H1N1 virus is now part of seasonal influenza virus circulation. As is customary, beginning in October 2010, the CDC will provide weekly reports of influenza surveillance information throughout the season with the publication of FluView available at www.cdc.gov/flu/weekly

The CDC recommends a three-step approach to fighting flu: vaccination, everyday preventive actions and the correct use of antiviral drugs if your doctor recommends them. The first and most important step in protecting against the flu is to get a flu vaccine each season.

The U.S. 2010-2011 influenza vaccine will protect against an H3N2 virus, an influenza B virus, and the 2009 H1N1 influenza virus that caused the first global pandemic in more than 40 years and resulted in substantial illness, hospitalizations and deaths. In the United States, the CDCs Advisory Committee on Immunization Practices recently recommended that everyone 6 months of age and older be vaccinated against influenza each season. Pregnant women, young children, and anyone with underlying health conditions like asthma, diabetes and neuromuscular diseases are at especially high risk for influenza-related complications and, therefore, should be vaccinated as soon as vaccine becomes available. Vaccine manufacturers are predicting an ample supply of influenza vaccine for the upcoming 2010-2011 U.S. influenza season.

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