The level of antibodies that has developed among the high-risk groups is not sufficient to control the infection and break the transmission of the virus, said Dr A C Mishra, Director of National Institute of Virology (NIV).

A study conducted by NIV shows that the risk of infection (seropositivity) was highest among schoolchildren during 2009 and those among the 15-19 age group were badly affected. While the good news is that this young population has developed antibodies against the virus, scientists are concerned that a higher level of immunity is required before the transmission can be broken.

The study on sero-epidemiology of pandemic influenza A (H1N1) virus infections in Pune was published in the August 25 issue of BioMed Central Infectious Diseases, 2010, journal.

The National Institute of Virology (NIV) had undertaken serosurveys among the risk groups and general population to determine the extent of pandemic influenza A (H1N1) 2009 virus infections. Mishra told The Indian Express that blood samples had been collected from the high-risk groups of doctors, schoolchildren, commuters, office goers and slum dwellers between August 15 and December 11, last year.

The survey studied more than 9,000 people from different age groups and found that the level of antibodies developed among the general population was less than 20 per cent.

For instance,among the 2,527 schoolchildren whose samples were collected in September last year, the risk of infection was as high as 25 per cent.

Dr B V Tandaley, scientist and study researcher at NIV, said 25 per cent of the children would be protected from the virus in the future and had developed antibodies. Similarly, in general practitioners, the serpositivity had increased from 4.9 per cent in August to 9.4 per cent in November and 15.1 per cent in December. By December the level of antibodies that had developed among this group was 15 per cent.