Effectiveness of DTaP Against Pertussis in ≤2-Year-Old Children — Linyi Prefecture, Shandong Province, China, 2017–2019

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC? Vaccine effectiveness (VE) is positively correlated with the number of administered co-purified diphtheria, tetanus, and acellular pertussis vaccine (DTaP) doses. A matched case-control study conducted in Zhongshan City revealed that the co-purified DTaP VE against pertussis-related illnesses in children aged 4–11 months was 42% for one dose, 88% for two doses, and 95% for three doses, respectively. WHAT IS ADDED BY THIS REPORT? The results of this study contribute to the current body of research. We found that the VE of co-purified DTaP against pertussis-related illness and hospitalization increased substantially, ranging from 24%–26% after one dose to 86%–87% after four doses. WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE? The results of this study underscore the significance of prompt and comprehensive immunization using co-purified DTaP to decrease the incidence of pertussis. Additionally, these findings offer evidence supporting the modification of China's pertussis vaccination approach.