On August 10, 2010, the Emergency Committee of the World Health Organisation (WHO) announced that in its view the world is no longer in phase 6 of influenza pandemic alert¹.

The new H1N1 virus has largely run its course, and the world has moved into the post-pandemic period. The decision is based on its assessment of the global situation, as well as reports from several countries that are now experiencing influenza. With the experience of past pandemics, it is expected that the H1N1 virus will 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, which is the case in New Zealand presently. 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 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 epidemics¹.

Notwthstanding the WHO announcement, Australia will remain in the "protect" phase until the present course of the 2010 seasonal influenza season better understood.

WHO recommendations for monitoring of respiratory disease activity during the post-pandemic period²

The WHO recommends that surveillance during the post-pandemic period include:

• monitoring for unusual events, such as clusters of severe respiratory illness or death;
• investigating severe or unusual cases, clusters or outbreaks to facilitate rapid identification of important changes in the epidemiology or severity of influenza;
• maintaining routine surveillance, including for influenza-like illness and cases of severe acute respiratory infections;
• continuing to use routine channels of data transmission for routine surveillance of respiratory disease;
• notifying WHO (including, where appropriate, notifications under the International Health Regulations) immediately if any of the following changes are detected:
  • sustained transmission of antiviral-resistant H1N1 2009 influenza
  • human cases of infection with any influenza virus not currently circulating in human populations
  • any notable changes in the severity or other epidemiological or clinical characteristics of the H1N1 2009 virus, including changes in the age distribution, the clinical appearance, proportion of cases requiring intensive management, or unexpected increases in numbers of cases.
• monitoring the H1N1 2009 virus for important genetic, antigenic or functional changes, such as antiviral drug sensitivity.

Vaccination remains important as a means of reducing the morbidity and mortality caused by influenza viruses².

References

1. WHO Recommendation: http://www.who.int/csr/disease/swineflu/notes/briefing_20100810/en/index.html

2. WHO Director General’s Statement: http://www.who.int/mediacentre/news/statements/2010/h1n1_vpc_20100810/en/index.html