The researchers argue that targeting children for vaccination would not only help protect those at greatest risk of exposure to the virus, but would also offer protection to unvaccinated adults. This so-called "herd immunity" effect would mean that significantly less vaccine would be necessary to help control the spread of the virus than if it were offered to everyone.

"Given that children are generally at particular risk from the disease, we believe that vaccination programmes for the young can be justified," says Dr House. "Although not sufficient to prevent a pandemic in themselves, such steps may support other control measures such as social distancing, antiviral drugs or quarantine."

The current study focuses on household transmissions. In the event of a disease outbreak, other modes of transmission are also likely, such as at work or on public transport. However, data for these modes is harder to come by. Professor Keeling and Dr House, together with colleagues at the University of Liverpool, are currently running wwwntactsurvey, a survey on contact patterns which they hope will help to quantify the relative importance of each context.

"We think it is unlikely that including these other contexts in our model will change the conclusion regarding vaccinating children," says Dr House. "In every city studied, households are seen to play a key role in the transmission of close-contact diseases like influenza."

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