Estimating diphtheria, acellular pertussis, tetanus vaccine (DTaP) effectiveness in preventing pertussis in children aged three months to six years old in Shenzhen area, China, case control study

VE increased with the number of doses administered. Although a gradual decline in VE over time was suggested after completing the primary series, conclusive evidence for waning immunity was limited by the precision of our estimates, which indicated a nonlinear trend. Our findings underscore the importance of ensuring universal completion of the four-dose DTaP series, which provided robust protection for at least the first four years of life.