Regular flu vaccine may help against H5N1: study

WASHINGTON (Reuters) - Ordinary seasonal flu vaccines may provide a small amount of protection against bird flu, Italian researchers reported on Wednesday.

Their study is among the first to support the idea that getting an annual flu shot may help people's bodies fight off the H5N1 virus, which has killed 210 people in 13 countries and infected 341.

Cristiana Gioia, Maria Capobianchi and colleagues at the National Institute for Infectious Diseases Lazzaro Spallanzani in Rome tested the blood of 42 volunteers who had been vaccinated against seasonal influenza.

In the laboratory, they added H5N1 virus to the blood and found that in some of the volunteers immune system proteins called antibodies acted against the bird flu virus.

They also found a few immune cells called CD4 T-cells seemed to recognize and act against H5N1 virus "and seasonal vaccine administration enhanced the frequency of such reactive CD4 T-cells," they wrote in the journal Emerging Infectious Diseases.

"Our findings indicate that seasonal vaccination can raise neutralizing immunity against (H5N1 avian influenza) virus," the researchers concluded.

This could help explain why H5N1, which only rarely affects people, is even rarer among the elderly, Gioia's team wrote.

"This finding may be explained by hypothesizing that older people, although not previously exposed to H5N1 subtype, may have gained protective immunity by previous infections sustained by circulating influenza virus strains," they wrote.

Several types of influenza circulate globally among people at any given time and these strains constantly mutate. This means flu vaccines have to be reformulated every year to match the mutations.

Health experts around the world are trying to boost rates of annual flu vaccination for two reasons -- because flu itself kills between 250,000 and 500,000 people a year, and also to help the world prepare for a pandemic.

These experts agree a pandemic is overdue, and fear H5N1 could cause the next one as it is constantly popping up among birds and a few people in Asia and Africa and among birds in Europe.

If more people get vaccinated against seasonal flu, companies will make more of the vaccine and can quickly turn production to match whatever strain of pandemic flu, including some version of H5N1, that may eventually occur.

(Reporting by Maggie Fox; editing by Stuart Grudgings)