Methods: We characterized the changes to transmission and epidemic trajectories among children and adults in a spatial context before, during, and after the winter holidays among aggregated physician medical claims in the United States from 2001 to 2009 and among synthetic data simulated from a deterministic, age-specific spatial metapopulation model.

Results: Winter holidays reduced flu transmission and delayed the trajectory of flu season epidemics. The holiday period is marked by a shift in relative risk of disease from children towards adults. Model results indicated that holidays delay epidemic peaks and synchronize incidence across locations, and contact reductions from school closures rather than age-specific mixing and travel produce these observed holiday flu dynamics.

Conclusions: Winter holidays delay seasonal influenza epidemic peaks and shift disease risk towards adults due to changes in contact patterns. These findings may inform targeted influenza information and vaccination campaigns during holiday periods.