Boys pass flu on to boys and girls to girls
Boys mainly pass on swine flu to boys, and girls to girls, a study has shown.
Research into how the virus was passed around a primary school showed transmission rates from boy-to-boy and from girl-to-girl were three times higher than between the sexes.
They were also five times higher between classmates then between children from different classes.
However, merely sitting next to a child with flu did not significantly increase the chances of catching it.
The results come from a joint British and American study of how swine flu spread around an elementary school in Pennsylvania, US.
The study, published today in the journal Proceedings of the National Academy of Sciences, involved 370 pupils from 295 households. Scientists used data from seating charts, timetables, bus schedules, nurse logs, attendance records and questionnaires to estimate rates of flu transmission in different settings.
Dr Simon Cauchemez, who led the study, from the Medical Research Council's Centre for Outbreak Analysis and Modelling at Imperial College London, said: "This is one of the most comprehensive studies to date on how a flu epidemic spreads between children in school, and it tells us a great deal about how social networks influence transmission.
"The data from this study will help us make more accurate models, which can help public health officials to handle epidemics effectively.
"For example, these new models could help us better understand whether and when it would be appropriate to close a school, or whether it might be better to close individual classes or grades."
The studied school was closed 18 days after the outbreak of swine flu, by which time 27pc of its pupils had already suffered symptoms.
According to the new analysis, transmission rates were falling at this stage and closing the school probably had little impact.