Factors Influencing the Size and Duration of School Varicella Outbreaks in Shanghai, China, in the Era of Voluntary Single-Dose Vaccination.

Varicella outbreaks continue to occur in schools. We assessed potential factors associated with the size and duration of 560 school-based outbreaks in Shanghai, China. Outbreaks occurring in primary and middle schools involved more cases and had longer durations, and conducting postexposure prophylaxis campaigns was an effective strategy for outbreak control.