WHO officially declares end to H1N1 pandemic

Dr Margaret Chan

The World Health Organisation (WHO) has declared an end to the influenza A (H1N1) pandemic but has called for continued vigilance, pointing out that pandemics, like the viruses that cause them, are unpredictable.

"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 Director-General Margaret Chan told reporters in Geneva yesterday.

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

Ms Chan said the committee had based its assessment on the global situation, as well as reports from several countries that are now experiencing influenza. She said she fully agreed 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," she said.

Ms Chan said that, 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 said.

"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," she said.

Ms Chan said that, globally, the levels and patterns of H1N1 transmission now being seen differed 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, she said.

According to her, 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," she said.

The WHO chief said that recently published studies indicated that 20–40% of populations in some areas had been infected by the H1N1 virus and thus had some level of protective immunity. Many countries report good vaccination coverage, especially in high-risk groups, and this coverage further increases community-wide immunity, she said.

"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," she said.

Ms Chan said that, based on available evidence and experience from past pandemics, it was likely that the virus would 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, she said.

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, she said.

"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," she said.

"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," she said.

Ms Chan said that, 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," she said.

As many as 1833 people have died in India since mid-June last year when the WHO declared the swine flu as a pandemic.

In the week ended August 8, 83 people had died of the influenza in different parts of the country.

NNN