Health Submiter

WASHINGTON (Reuters) - An experimental bird flu vaccinethat uses a common cold virus and bits of DNA from the H5N1virus appears to stimulate an immune response in mice, U.S.researchers said on Thursday.

They said their experiment is a first step towardsdeveloping a next-generation bird flu vaccine that does notneed to be grown for months in chicken eggs and that couldprotect against mutated versions of the virus.

“We want to have a vaccine that can be stored in advanceand have the potential to provide protection for a period oftime until we can change the vaccine to match the latest formof avian influenza,” said Suresh Mittal of Purdue University inIndiana, who worked on the study.

“The combination of flu genes that we've used to producethe vaccine, I think, will provide that capability.”

The H5N1 avian influenza virus currently mostly affectsbirds 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 peoplesince 2003, killing 240 of them, according to the World HealthOrganization.

At least 16 companies are working on vaccines to preventbird flu infection in people, but the process is problematic.Flu vaccines are hard to make because they must be grown inchicken eggs for months, and the viruses themselves mutateevery year.

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

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

Mittal, Mary Hoelscher of the U.S. Centers for DiseaseControl and Prevention and colleagues worked with H5N1 virussamples from Vietnam and Indonesia to make a vaccine that theyhoped would work against even “drifted,” or mutated, strains.

They used a common cold virus, known as an adenovirus, tocarry H5N1's hemagglutinin gene, which give flu strains the “H”of their names.

Most current flu vaccines also focus on hemagglutinin.

They also used another gene called nucleoprotein or NP,which has not been used in flu vaccines. The hope is that theNP gene will both promote an immune response against flu, andperhaps be a bit more stable than the highly mutation-pronehemagglutinin.

So far the researchers have only tested mice, but thevaccine caused a strong immune response that lasted at least ayear.

“In humans we want a vaccine to be fully effective for atleast a year,” Mittal said in a statement.

“This approach may prevent severe illness and death orshorten the course of future infection with H5N1 virus strainsthat are antigenically distinct from currently circulatingstrains, and it may offer stockpiling advantages that overcomethe limitations associated with storage of egg-derivedvaccines,” the researchers wrote.

Their technology has been licensed to PaxVax Inc, aprivately held San Diego-based corporation.

(Reporting by Maggie Fox; Editing by Will Dunham and EricWalsh)