Although there is no laboratory evidence that human infection with bird flu in Vietnam is occurring more frequently or that the virus is spreading readily among humans, the UN health agency today maintained its current level of alert over a potential pandemic, which in a worst case scenario could kill tens of millions of people worldwide.
The World Health Organization (WHO) said reports that it had downgraded its assessment of the pandemic threat, first made at the start of the current outbreak in South-East Asia in January 2004, were unfounded.
WHO issued its statement following the visit to Vietnam of an agency team of international experts sent at the Government’s request to search for evidence that the H5N1 virus had changed its behaviour in ways consistent with an improved, though not yet efficient, ability to spread directly from one human to another. In its preliminary findings the team did not confirm such a change.
Firm evidence of improved transmissibility would be grounds for moving to a higher level of pandemic alert. Because of the huge consequences of such a change, WHO said it was following a cautious approach that combines heightened vigilance for new cases with immediate international verification of any suggestive findings.
WHO has repeatedly stressed the need for scientists to determine possible changes in the behaviour of H5N1 to assess the risk of a human pandemic. The so-called Spanish flu pandemic of 1918-1920, unrelated to the present virus, is estimated to have killed between 20 million and 40 million people worldwide.
WHO is concerned that continuing transmission from birds to humans might give avian and human influenza viruses an opportunity to exchange genes, facilitating a pandemic.
Overall there have been more than 100 reported human infections, about 50 of them fatal, since the first case linked to widespread poultry outbreaks in Viet Nam and Thailand was reported in January last year. Nearly 140 million domestic birds have died or been culled over the past year in South-East Asia in an effort to curb the spread of the disease.