And it could reduce some types of flu by 70 per cent.

Because toddlers can come into close contact with the elderly, experts believe that targeting this age group would dramatically reduce the number of pensioners struck down each year.

The study by the Health Protection Agency estimated the effects of vaccination in the under-twos, under-fives and under-16s.

If everyone under 16 had it, incidence of both influenza A and B strains could drop by more than 90 per cent.

Immunising those between six months and two years would reduce flu in the population by between 11 per cent and 35 per cent, depending on the strain.