A recent study supports a theory that seasonal flu vaccines may offer a slight amount of protection against bird flu, Italian researchers reported Wednesday.

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 antibodies acted against the bird flu virus.

They also found a few immune cells called CD4 T-cells seemed to recognize and act against the 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.

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.

(Agencies via Xinhua News Agency December 28, 2007)