Regions. Most (83.3%) studies on pneumonia incidence were conducted in Northeast and Southeast China. The incidence of pneumonia in children ,5 years of age in Northeastern China (range: 0.06±0.27 episodes per person-year) [16, 18, 19, 26] , was lower than southern China (range: 0.32±0.66 episodes per personyear), which includes the Southeast, South Central, and Southwest regions (Table S2) [24, 27, 28] . There were no studies exclusively in the North Central or Northwest regions. One multi-site study showed that pneumonia incidence among children ,5 years of age was higher in Southern than in Northern provinces (0.057 versus 0.013 episodes per person-year in southern Yunnan and northern Qinghai, respectively) [21] . A multi-site study in 1986 reported that pneumonia incidence in children ,14 years of age in Eastern China (range 0.041±0.057 episodes per person-year) was higher than in Western and Central China (range 0.032±0.035 episodes per person-year) [25] .