In an Asian clinical trial by GlaxoSmithKline involving 1,206 adults in Hong Kong, Singapore, Taiwan and Thailand, the vaccine produced antibodies that neutralized the H5N1 virus found in Vietnam and also the variant now dogging Indonesia, the company claimed yesterday.

"The vaccine was made using the Vietnamese strain," said Albert Osterhaus, the head of virology at the Erasmus Medical Centre in the Netherlands.

"In principle, there is a very broad antibody reactivity that is being induced. These are neutralizing antibodies and they do correlate with protection."

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Osterhaus was not involved in the study but is familiar with the results and methodology.

An earlier GSK study in Europe showed the vaccine to be effective in protecting against two other H5N1 subtypes, in China's Anhui province and in Turkey.

For years, experts have warned that a flu pandemic was long overdue, and many have held up the H5N1 virus as a prime candidate because people have no immunity against it. The virus has infected at least 368 people in 14 countries since 2003 and killed 234.

A vaccine to protect against a flu pandemic can only be made four to six months after the start of such a disaster, when the virus strain has been identified. People need protection in those initial months of a pandemic, and drug companies are in a race to design what are known as "prepandemic" vaccines.

GSK's prepandemic vaccine uses a very low dose of antigen. Antigens are substances like toxins, viruses and bacteria, which stimulate the production of antibodies. But they can be difficult to culture, and scientists have tried to fix that by using boosters, or adjuvants.

Volunteers in the GSK trial received two shots of adjuvanted vaccine 21 days apart, and tests showed the presence of antibodies that neutralized the Vietnam and Indonesian H5N1 strains.

Osterhaus, however, voiced a note of caution - that a pandemic may be triggered by a different virus, saying "the thing with flu is we have to expect the unexpected.

REUTERS