A U.S.-based drug company says preliminary tests on a bird flu vaccine suggest it is safe, well-tolerated and could be effective against mutated strains of the virus.

Baxter International, based near the city of Chicago, announced Wednesday that early clinical trials of its vaccine show it can trigger development of antibodies to neutralize different strains of the H5N1 virus.

The company says it has tested its vaccine on 270 healthy adults. Side effects were reported to be similar to traditional flu vaccines - soreness, headaches and fatigue. Baxter says the preliminary results must be confirmed in a larger study.

The World Health Organization says since 2003, at least 148 people worldwide have died of bird flu after contracting it from infected birds.

Health experts fear the virus could mutate into a form that could easily pass from person to person and cause an epidemic.

Some information for this report was provided by Reuters.