Background: There is limited information on differences in the dynamics of influenza transmission during time periods when schools are open compared with periods when they are closed.
Methods: Data on school openings, influenza surveillance, and absolute humidity were incorporated into a regression model to estimate the increase in the reproductive number for the 2009 A(H1N1) influenza pandemic associated with the opening of school in 10 US states.
Results: The estimate for the average increase in the reproductive number for the 2009 A(H1N1) influenza pandemic associated with the beginning of the school year was 19.5% (95% credible interval = 10%-29%).
Conclusions: Whether schools are open or closed can have a major impact on community transmission dynamics of influenza.