Today, Dr. Margaret Chan, the Director General of the World Health Organization announced that Phase 6 of the H1N1 Pandemic is officially over and the world has entered into the post pandemic period or phase.

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Dr. Chan made this announcement after the Emergency Committee met earlier today…“The world is no longer in phase 6 of influenza pandemic alert. We are now moving into the post-pandemic period. The new H1N1 virus has largely run its course.”

What does post-pandemic mean? How does WHO know that the pandemic is over?

The H1N1 pandemic was characterized by the emergence of a new influenza virus to which many people had no pre-existing immunity. It caused unusual and extensive outbreaks of disease in the summer months in many countries and very high levels of disease in winter months. It was also characterized by an almost complete dominance of the pandemic virus over other seasonal influenza viruses, and by unusual clinical patterns where the most severe cases occurred most often in younger age groups.

The world is now moving into a situation where the virus has spread to all countries, when many people in all age groups in many countries have some immunity to the new virus, and where no large and unusual summer outbreaks have occurred in either Northern or Southern Hemispheres, and where seasonal influenza A (H3N2) and influenza B viruses are being reported in many countries. Based on this overall picture, the evidence is strong that the recent influenza pandemic patterns are transitioning towards seasonal patterns of influenza. However, some countries, such as India and New Zealand, are continuing to experience significant levels of influenza H1N1 (2009), and national authorities in these countries will need to maintain implementation of outbreak response measures for some time to come. It is important to realize that the H1N1 (2009) virus can be expected to remain for many years and that individual influenza seasons themselves can be highly variable. In some years, the impact can be mild while in other years it can be quite severe.

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In the post-pandemic period, cases and outbreaks due to the H1N1 (2009) virus are expected to continue to occur.

In addition, it is most likely that for some period of time, younger age groups, including pregnant women, will continue to be affected disproportionately by severe disease from H1N1 (2009), including viral pneumonia. It is impossible to predict if younger people will remain at higher risk over the long term for severe disease or whether and when this will change. Given this picture, it will remain important for people to continue to take prudent steps to protect themselves. Actions to generally reduce risks of influenza infection, such as through use of vaccines and hand and respiratory hygiene, will also reduce the risks from H1N1 infection specifically.

WHO recommends the use of influenza vaccine to protect people as a safe and effective countermeasure to reduce the chances of developing severe illness. The H1N1 (2009) influenza virus is expected to continue to circulate worldwide for many years, and many people are still susceptible to infection. The H1N1 (2009) virus caused most of its severe or fatal disease in younger people, both those with chronic conditions as well as healthy persons, and caused many more cases of viral pneumonia than are normally seen with seasonal influenza. WHO particularly recommends vaccination for health care workers and groups at high risk for severe disease.