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H5N1 in Vietnam: Pandemic Threat Remains Unchanged

By Eric Toner, M.D., July 7, 2005

Last week an international team of experts completed a visit to Vietnam. The purpose of their visit was to determine whether the pandemic alert level should be raised. This investigatory visit was prompted by an urgent WHO consultation held in Manila in May, which was called in response to epidemiologic evidence that suggested the possibility of limited but increasing human-to-human transmission.

News stories have widely reported that the team concluded that the pandemic threat was less than previously thought. This is not true according to the WHO. In fact, the team was specifically tasked with finding confirmatory laboratory evidence of community-acquired infection. Although they did not find this evidence, these tests are preliminary and the specimens will be retested.

Several points are worth noting: First, absence of evidence is not evidence of absence. The fact that these tests did not demonstrate community transmission does not mean it is not occurring. The epidemiologic evidence that prompted this visit still exists. Second, this was far from a comprehensive survey of the country. The WHO team consisted of only a half dozen individuals who were in Vietnam for about 3 weeks.

Sporadic cases of human H5N1 continue to occur in Vietnam. There have now been 108 confirmed cases of H5N1 in Southeast Asia over the past year and a half, 64 of which have occurred in the past 6 months. The case fatality rate is now 50% and appears to be decreasing, at least in northern Vietnam. There continue to be references to unpublished serological studies that suggest that there may be a significant amount of unrecognized H5N1 infection in Vietnam.

Meanwhile, outbreaks of H5N1 in wild migratory birds continue in western China. The origin of these outbreaks is unknown, but it is clear that as these birds start to migrate to the Indian subcontinent in the next 2 months, the risk of further spread of the disease increases.

While the news of the WHO team’s visit to Vietnam is welcome, a much more vigorous international effort is needed. It is critical that a comprehensive study of the extent of H5N1 infection both in humans and wild birds be done immediately and that there be a much more robust ongoing surveillance regime.