Effects of school breaks on influenza-like illness incidence in a temperate Chinese region: an ecological study from 2008 to 2015

Chu, Yanhui; Wu, Zhenyu; Ji, Jiayi; Sun, Jingyi; Sun, Xiaoyu; Qin, Guoyou; Qin, Jingning; Xiao, Zheng; Ren, Jian; Qin, Di; Zheng, Xueying; Wang, Xi-Ling

Age-specific population sizes in Xicheng District were collected from China's 2010 population census. We assumed that the age-stratified population remained constant over the study period. We ignored the immunised population as the influenza vaccination coverage was below 3% in the general population. School calendars for winter/summer breaks of primary and secondary schools in Beijing were obtained directly from Beijing Municipal Education Commission. School calendars were usually announced ahead of each academic year. Winter breaks were often in January and February, which lasts for 4 weeks and covered the 7-day statutory holidays for national Chinese New Year. Summer breaks are in July and August, which last for 7 weeks. The exact starting dates of winter/summer school breaks varied slightly across years and schools. On average, winter breaks in Beijing started at the 5th week and ended at the 8th week, while summer breaks started at the 29th week and ended at the 35th week.