Influenza A(H1N1) 2009
Post-pandemic phase and the H1N1 2009 situation in the Western Pacific Region
11 August 2010
On 11 June 2009, the World Health Organization raised the level of influenza pandemic alert from phase 5 to phase 6, declaring the beginning of the influenza A(H1N1) 2009 pandemic. 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.
On 10 August 2010, WHO Director-General Dr Margaret Chan announced that the H1N1 2009 influenza virus had moved into the post-pandemic phase. This means that "levels of influenza activity have returned to the levels seen for seasonal influenza in most countries with adequate surveillance". It is expected that the pandemic virus will increasingly behave more like a seasonal influenza A virus. Based on current global epidemiological and virological data, the evidence is strong that the recent influenza pandemic patterns are transitioning towards seasonal patterns of influenza.
Overall situation in the Western Pacific Region
From April 2009 to July 2010, more than 250,000 cases and 1,800 deaths from laboratory-confirmed pandemic influenza A(H1N1) 2009 were reported from 34 countries and areas in the Region. The majority of the cases recorded occurred in children and young adults. Most experienced mild illnesses requiring no medical treatment at all; however, a small proportion of cases developed complications and required hospitalization.
Currently, the pandemic H1N1 2009 virus is still circulating in the Region, especially in southern hemisphere countries and some tropical countries and areas.
Ongoing localized outbreaks
In most countries and areas of the Region it appears that the levels of influenza activity are similar to previous pre-pandemic influenza seasons. However, localized outbreaks of different magnitude are ongoing.
New Zealand is seeing a significant second wave of pandemic influenza, particularly in areas that were not as greatly affected last year, with higher levels of hospitalization in some of these areas, including intensive care cases. Some Pacific Islands and areas may also be at risk from a significant second wave of H1N1 2009-associated illness as they did not experience intense transmission last year.
Given this picture, it is important for countries to remain vigilant and alert for infections and outbreaks and to continue to take steps to protect their populations against influenza.
Where to get more information
During public health emergencies, it is important to seek accurate information about the situation. For official information on this evolving situation and for technical and communication guidance for health administrators, health professionals and the general public, please click on the following links: