WHO | H1N1 in post-pandemic period

H1N1 in post-pandemic period
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.

WHO recommendations for the post-pandemic period


These are the views of members of the Emergency Committee, which was convened earlier today by teleconference.

The Committee based its assessment on the global situation, as well as reports from several countries that are now experiencing influenza. I fully agree with the Committee’s advice.

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 behaviour 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.

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 20–40% 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.

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, 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.

As I said, pandemics are unpredictable and prone to deliver surprises. 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.

I will be happy to answer your questions.

WHO | H1N1 in post-pandemic period