As the country gears up to the threat of bird flu, a new study has found that three strains of influenza viruses are prevalent in the country throughout the year, but the dreaded H5N1 strain has not been found so far. 

Thus, the elderly and those with reduced immunity due to diseases such as heart disease or chronic-lung disease should be given the influenza vaccine to protect them against influenza viruses, scientists suggested. 

Vaccination is also expected to prevent the crucial change in the bird-flu virus (H5N1), which experts fear would make it transmissible from humans to humans, Dr Lalit Dar from the AIIMS' department of microbiology, who also participated in the research, said. 

Some studies suggest that severity of H5N1 infection may be reduced if people are vaccinated by the influenza vaccine, he said. 

So far the H5N1 strain is not transmitted from human to human. But it is feared that when humans are infected both by this strain and other influenza virus strain, an exchange of genetic material between the two may result in the dreadful strain which would get transmitted among humans. 

"Strains of influenza viruses were found in the country throughout the year except in the month of May in the study undertaken by the Indian Council of Medical Research with support from the World Health Organisation," Dar said.