Experimental U.S. bird flu vaccine uses cold virus

WASHINGTON (Reuters) - An experimental bird flu vaccine that uses a common cold virus and bits of DNA from the H5N1 virus appears to stimulate an immune response in mice, U.S. researchers said on Thursday.

They said their experiment is a first step towards developing a next-generation bird flu vaccine that does not need to be grown for months in chicken eggs and that could protect against mutated versions of the virus.

"We want to have a vaccine that can be stored in advance and have the potential to provide protection for a period of time until we can change the vaccine to match the latest form of avian influenza," said Suresh Mittal of Purdue University in Indiana, who worked on the study.

"The combination of flu genes that we've used to produce the vaccine, I think, will provide that capability."

The H5N1 avian influenza virus currently mostly affects birds and is sweeping though flocks in many parts of Asia, Africa and occasionally in Europe.

It can rarely pass to humans and has infected 381 people since 2003, killing 240 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 the viruses themselves mutate every year.

The seasonal flu vaccine must be reformulated every year and no one knows what would happen if H5N1 mutated into a form that people could transmit easily to one another.

If a pandemic broke out, using current technology it would be close to a year before anyone could be vaccinated.