Bird flu vaccine gives strong protection in mice

HONG KONG (Reuters) - An experimental bird flu vaccine that uses DNA from various strains of the H5N1 virus appears to trigger a strong immune response in mice after it is injected straight into the muscles, a study has shown.

In the journal Cell Research, scientists in Taiwan and the United States said the vaccine protected mice fully against H5N1 strains from Vietnam, Turkey and China's eastern Anhui province.

"We injected it into mice and after more than a week, the mice were immunized and we challenged the mice with live virus strains from Vietnam, Indonesia, Turkey and Anhui," Chi-Huey Wong from The Genomics Research Center in Taiwan's Academia Sinica told Reuters by telephone.

"The mice were fully protected from the strains from Vietnam, Turkey and Anhui, while 80 percent (of mice) were protected from the Indonesian strain, but that's still very high."

Another group of mice which were not immunized all died within days of being infected with lethal doses of the virus.

Vaccines using DNA are a departure from the traditional way vaccines are made -- painstakingly grown in chicken eggs, which could well be in very short supply in the case of a pandemic.

The H5N1 avian influenza virus currently mostly affects birds and is endemic in flocks in many parts of Asia. It has also swept through flocks in Africa and occasionally in Europe.

It rarely infects humans but when it does, the casualty toll is heavy. Since 2003, it has infected 385 people, killing 243 of them, according to the World Health Organization.

At least 16 companies are working on vaccines to prevent bird flu infection in people, but the process is problematic. Flu vaccines are hard to make because they must be grown in chicken eggs for months, and viruses mutate all the time.

Wong said their vaccine was designed using a "consensus DNA sequence" that was based on varieties of H5N1 viruses found since 1997, when the virus first infected people in Hong Kong.

The scientists hope to take their experiment a step further into human clinical trials once approval is given.

(Reporting by Tan Ee Lyn; Editing by Paul Tait)