A big pertussis outbreak in a primary school with high vaccination coverage in northern China: An evidence of the emerging of the disease in China

Abstract Background A big pertussis outbreak occurred in a primary school with high vaccination coverage in northern China. An investigation was carried out in order to calculate the attack rate and identify the risk factors. Methods Between May 12 and July 29, an investigation was carried out in the primary school, which included 383 students and 27 teachers. Three definitions were used to distinguish the cases: confirmed, epidemiologically linked and suspected cases. A total of 232 blood samples were collected and examined by ELISA among healthy children in another primary school. Results A total of 138 suspected pertussis cases were counted, of which 116 students were confirmed. The attack rate among students was as high as 30.29%. The pertussis outbreak lasted 88 days, and had quaternary cases of transmission. Migrant children were almost four times as likely to catch the disease as local children ( p  = 0.005). In addition, students who had received the last dose of pertussis vaccine more than 4 years prior were three times more likely of becoming ill than those less than 4 years ( p  = 0.006). The average level of antibodies to pertussis was 30.99 IU/mL among healthy children. No statistically significant difference was observed between DTaP and DTwP ( p  = 0.843). Conclusions This pertussis outbreak in a primary school with high vaccination coverage was an evidence of the pertussis resurgence in China. The major risk factor we identified was the waning of immunity in the years after pertussis vaccination. Booster vaccination for students should be given.