updated 3/6/2007 9:00:03 AM ET 2007-03-06T14:00:03

A potential flu pandemic vaccine based on one strain of the H5N1 bird flu works against other versions of the virus as well, the vaccine’s manufacturer said Monday.

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GlaxoSmithKline PLC announced new study results showing that even though their pre-pandemic vaccine uses an H5N1 strain from Vietnam, it reacts against the Indonesian version of the virus. The vaccine was developed with an adjuvant (a component used to stretch the active ingredient) exclusive to GlaxoSmithKline. Results proved the adjuvant could increase the number of vaccine doses by 10 times, which would be crucial in a pandemic situation, when demand would far outstrip supply.

One GlaxoSmithKline study measured the levels of antibodies in 400 adults, after some of them were given two shots of the vaccine. People inoculated with the vaccine tested had strong antibody levels that could potentially fight off the H5N1 Indonesian virus in addition to the Vietnamese virus.

While encouraging, this is not the first time that cross-protection has been seen. Other companies, such as Novartis SA and Sanofi Aventis have previously reported similar results. More than a dozen companies worldwide are working on potential flu pandemic vaccines.

“These results are good news, but we’re still in the early days and we don’t really know which of the vaccine formulations are the better ones,” said Dr. Alan Hay, director of the World Health Organization’s Collaborating Center laboratory in Britain. Many basic questions regarding H5N1 vaccines remain unanswered, such as the exact threshold of antibodies necessary for protection.

'Prime and boost'
But the broader a vaccine’s protection, the more useful stockpiles might be, since it is unknown which virus might spark the next flu pandemic. Experts believe H5N1 is the most likely candidate to mutate into a pandemic virus, but another flu subtype could ultimately be responsible. To date, H5N1 has killed at least 167 people worldwide.

If a vaccine protects against different H5N1 strains, people could theoretically be pre-vaccinated before getting a booster shot with a new formulation containing the pandemic strain, once the global outbreak strikes. A study last year found that people vaccinated with a bird flu shot using the 1997 H5N1 Hong Kong strain had an immune advantage when given another H5N1 vaccine based on the Vietnam strain, seven years later. This “prime and boost” principle could save the lives of doctors, nurses, and other first responders in a global flu outbreak.

“This anticipated protection is still hypothetical,” cautioned Dr. Marie-Paule Kieny, director of WHO’s Initiative for Vaccine Research. Authorities must weigh the risks of immunizing healthy people with a vaccine that has unknown side effects.

Still, if scientists can create an H5N1 vaccine that fights other versions of the virus, resolving the continuing virus stand-off between Indonesia and WHO — Indonesia refuses to share samples unless WHO agrees to certain conditions — could be less important.

But that would hardly be ideal. “If we had a vaccine that protected against all H5 viruses, maybe we wouldn’t care about what new isolates (viruses) there might be,” said Dr. John Treanor, a vaccines expert at the University of Rochester. “But we’re not at that point yet,” he said. “We don’t know enough about H5N1 and we need to keep a very close eye on it.”

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