Published online 11 June 2009 | Nature | doi:10.1038/news.2009.564


Flu pandemic underway

Countries prepare for the long haul in combating novel H1N1 strain.

Margaret Chan, the director-general of the World Health Organization (WHO), has officially declared the first global influenza pandemic in 41 years, for the A(H1N1) virus.

Whether the WHO decision will change much in practice remains to be seen, as the world has clearly been in a pandemic for weeks. The big question now is how severe the pandemic will be. For the moment, WHO puts it as "moderate", and Chan pointed out it could get worse both with time and place.

Children are disproportionately affected by the novel H1N1 virus.ASSOCIATED PRESS / Arnulfo Franco

"The world is now at the start of the 2009 pandemic," she said. That makes it the fourth flu pandemic in a century, after 1918, 1957 and 1968. "The scientific criteria for a pandemic have been met," she said; on 11 June the WHO moved to the topmost of its pandemic threat scale, phase 6, which indicates sustained community-level outbreaks in two or more countries in one other WHO region beyond initial community spread in one WHO region. "Further spread is considered inevitable," she said.

"The declaration of a pandemic does not suggest there is a change in the behaviour of the virus, just that it is spreading in more parts of the world," added Thomas Frieden, director of the US Centers for Disease Control and Prevention in Atlanta, Georgia. "It does send a strong message that the virus is here, in all likelihood here to stay."

Behind the scenes

In recent weeks, the WHO had been under pressure from its member states to hold off from declaring a pandemic, over concerns that countries might overreact. Most of the concerns — for example, that people might worry about eating pork or that governments might cull pig herds or introduce trade embargoes, travel bans or border controls — had more to do with trade than with public health, Keiji Fukuda, WHO's interim assistant director-general for health security and environment, said on 9 June.

One health concern, though, is the risk that anxious people without H1N1 infections might flood hospital emergency rooms and so divert resources from those with real health-care needs. Chan reiterated that restrictions on travel, or border controls, were ineffective at stopping spread, and called for countries to abstain from trade bans.

On 29 April, WHO moved its assessment of the pandemic threat to phase 5 on its six-point scale, indicating that the new virus had caused "sustained community level outbreaks in two or more countries in one WHO region" after initial outbreaks in the United States and Mexico. Until today, that is where it had sat.

The virus has spread to 74 countries, with evidence of community spread in Australia, the United Kingdom and Chile, among others. More than 28,700 cases have been confirmed by lab tests worldwide — likely only a fraction of the total number — with 144 deaths documented.

It's official

After a 10 June teleconference among Chan and affected governments, WHO's emergency committee met at midday today and recommended raising the level to 6. Chan officially informed WHO member states during the afternoon.

On 9 June, Fukuda all but agreed that a pandemic declaration was inevitable and that the question was more one of preparing countries "to know how to take that news". Such preparation would mean offering clearer guidance to countries on how they should adapt their pandemic plans — largely built around the deadlier H5N1 avian influenza virus — to the current virus and taking time to explain to the media and others what a pandemic meant.

The WHO expects national responses to remain the same for phases 5 and 6. Both call for "each country to implement actions as called for in their national plans" and to be ready for an "imminent response". Many countries had already rolled out their pandemic plans as of Phase 5 and will tailor the extent of their response not to the declaration of Phase 6, but to the severity of the pandemic as it moves forward over the next few months and years.

That remains unpredictable. The clinical picture as the virus has spread in the Southern Hemisphere remains similar to that seen in the Northern: mostly illnesses from which people recover by themselves, but also cases of life-threatening viral pneumonia, where the virus itself, and not secondary bacterial infections, causes respiratory distress or failure.


But the WHO remains deeply concerned that half the deaths continue to be in healthy younger people, as in past pandemics and H5N1 avian flu. "It is significantly different to seasonal flu," said Chan.

The first vaccine will not start flowing until September. Chan called for international solidarity so that "no countries would be left behind without help", pointing out that developing countries with poor health infrastructure, and whose populations often have high levels of underlying diseases, risk being hit hardest. "We are all in this together, and we will all get through this together."

For Nature 's ongoing coverage of the H1N1 outbreak, see 

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