WHO declares H1N1 swine flu an official pandemic

The World Health Organization (WHO) has today declared H1N1 swine flu an official pandemic — level six in the WHO’s rating scheme. This means the world’s vaccine industry can now switch from making vaccine for ordinary flu to pandemic vaccine.

Debora MacKenzie writes that companies, however, are not likely to change production until they have finished their current production run of ordinary flu vaccine in July or August. This will be the case, even though that vaccine will be useless if swine flu behaves like previous pandemics and replaces the current, ordinary flu viruses. The WHO’s declaration of level six, though, activates a slew of government pre-orders for pandemic vaccine. These will take precedence over recent orders for H1N1 vaccine. Countries that do not have pre-orders will also face delays.

The WHO cautioned against over-reaction, as most cases of H1N1 have so far been relatively mild. The organization had been under pressure not to declare a pandemic for such a mild virus. WHO officials have insisted, however, that a flu pandemic is defined by how fast a novel flu virus spreads, and who it affects, not necessarily how severe it is. This is partly because the same virus can be mild in some people and severe in others, and partly because it can evolve. In 1918, the last pandemic H1N1 started out mild, but its second wave was much more severe.

MacKenzie writes that pandemic flu can also kill healthy young adults, not the very young and old like ordinary flu. “Approximately half the people who have died from this H1N1 infection have been previously healthy people,” Keiji Fukuda, head of flu at the WHO, said on Tuesday, adding this had given the organization “the most concern.” “It is of greatest importance to continue surveillance of the virus worldwide,” David Heymann, until recently head of health security at the WHO, told New Scientist. “Science cannot predict what course this virus will take as it continues to spread in humans.”

The WHO’s pandemic levels are based on how widely a novel flu virus is spreading. Level six means a virus is spreading widely in the community in at least two continents. There has been evidence for this for a week or more.

By 3 June, swine flu had reached every WHO region, and it has now been detected in 74 countries. Case numbers have been increasing steadily in Australia since late May, and rose fourfold to 1,224 in the past week - mainly in Victoria State, which has reported community spread.

There has been evidence of undetected community spread in Scotland, and on Thursday, Hong Kong closed primary schools to slow down community spread.

In May several countries, including the UK and Japan, asked the WHO to delay declaring level 6, fearing trade and travel disruption, and the swamping of hospitals by the “worried well,” in response to a virus that is not yet causing severe illness.

A poll in New York City this week suggested that hundreds of thousands of New Yorkers have had H1N1, but only 0.1 percent needed hospitalization. Ordinary winter flu has death rates around 0.2 to 0.35 percent.

Fukuda, though, warns severity can vary from place to place. The Canadian province of Manitoba closed schools this week after severe H1N1 among First Nations (Indian) people strained hospital capacity. Aboriginal communities, also hard hit in 1918, could be suffering more due to poverty or higher prevalence of TB, raising concerns for the impact of H1N1 in poor countries.

The southern hemisphere is now having its regular winter flu season: H1N1 cases rose from 411 to 1,694 in Chile this week. But unlike the northern hemisphere, H1N1 in the south is circulating alongside, and competing with, the ordinary, seasonal human flu viruses. The future of this pandemic now depends on how well it does.