Experts fight H5N1 bird flu using smallpox vaccine

HONG KONG, March 1 (Reuters) - Scientists in Hong Kong and the United States have developed an experimental H5N1 bird flu vaccine for people by piggybacking it on the well-tested and highly successful smallpox vaccine.

Initial tests on mice showed the vaccine to be highly effective, they told a news conference in Hong Kong on Sunday.

"It produced a lot of (H5N1) antibodies and the speed of antibody response was far higher with this strategy than the Sanofi one," said Malik Peiris, a microbiologist and bird flu expert at the University of Hong Kong.

Peiris was referring to Sanofi-Aventis's


H5N1 bird flu vaccine for humans, which has been approved for use in the United States.

In an article published in the current Journal of Immunology, the experts from Hong Kong and the U.S. National Institutes of Health described how they inserted five key components of the H5N1 virus into the smallpox vaccine.

"We put in many other proteins into that vaccine; we are using it like a carrier, if you like, a piggyback," Peiris said.

The vaccine uses a Vietnam strain of the H5N1 virus and appeared to be broadly protective. Mice which were inoculated with it successfully fought off an Indonesian strain of H5N1, according to the scientists.

Since 2003, the H5N1 avian influenza virus has infected 408 people in 15 countries and killed 254 of them. It has killed or forced the culling of more than 300 million birds as it spread to 61 countries in Asia, the Middle East, Europe and Africa.

While H5N1 rarely infects people, experts fear it could mutate into a form that people could easily pass to one another, sparking a pandemic that could kill tens of millions and topple the global economy.

Smallpox was eradicated worldwide in 1979 and the experts are hoping that their novel H5N1 vaccine can ride on the various advantages of the smallpox vaccine.

The smallpox vaccine is very cheap, has a long shelf-life of several years and does not require highly sophisticated laboratories, making it easier for poorer countries to produce.

"It is very stable and you can pack them off to developing countries and use them. They require refrigeration but it is less critical than other vaccines," Peiris said.

"Smallpox production capacity has gone down but many countries have the technology and the expertise to do it, and if necessary, it can be very quickly scaled up."

"But for other strategies (of producing H5N1 vaccines), it is not possible to rapidly set up manufacturing plants all over the world as they require very specialised plants."

However, it will take at least a few more years before the vaccine would be ready for the market. It must be tested next in ferrets, then monkeys, before human clinical trials can be carried out. (Editing by Kim Coghill)