BANGKOK (Reuters) - Animals that have previously beenvaccinated against seasonal flu appear to respond far quickerto experimental H5N1 bird flu vaccines, a study has found.

Many doctors believe that seasonal flu vaccines offerlittle or no protection against the H5N1 virus, which expertssay may unleash a pandemic that could kill millions of people.

But a study by biotechnology firm MedImmune Inc, whichproduces influenza vaccine, found that ferrets that had beenvaccinated against seasonal flu appeared to be more responsivewhen they were later administered the H5N1 vaccine.

"If you have previously received normal seasonal fluvaccine, you may have better response to the H5N1 vaccine,"MedImmune´s scientist Hong Jin told a bird flu conference in Bangkok.

Researchers at the National Institute for Infectious Diseases in Rome published a study in the journal Emerging Infectious Diseases in December showing that ordinary seasonal flu vaccines may provide a small amount of protection against bird flu.

Their study was among the first to support the idea thatgetting an annual flu shot may help people´s bodies fight offthe H5N1 virus.

In the laboratory, they added H5N1 virus to the blood andfound that in some of the volunteers immune system proteinscalled antibodies acted against the bird flu virus.

In the MedImmune study, a group of ferrets was givenseasonal flu vaccine, while a control group of ferrets weregiven nothing.

Forty days later, both groups were given H5N1 vaccinesdesigned using seed virus taken from outbreaks of the diseasein Hong Kong in 2003 and Vietnam in 2004.

They were then monitored for the production of H5N1antibodies.

"We found much more response in ferrets that received(seasonal flu) vaccine before, whereas in control ferrets, youdon´t see the response," Hong told Reuters.

Huge volumes of antibody producing cells were seen in theferrets that had both vaccines on day 45, but there was noantibody response in the control group, MedImmune said.

"Maybe the (seasonal flu) vaccine can induce immuneresponse that can speed up response to H5 vaccine," Hongexplained.

Both types of vaccines were administered using nasal spray.MedImmune first introduced its nasal spray influenza vaccine in2003.

(Reporting by Tan Ee Lyn; Editing by Caroline Drees)