In this issue of Pediatrics, the vaccine research group at Kaiser Permanente Northern California (KPNC) contributed another important article outlining the challenges of pertussis control in a highly vaccinated population.1 Nearly one-half million children born between 1999 and 2016 and managed at KPNC from 2006 to 2017 were evaluated. Of those immunized children, all had received only diphtheria-tetanus-acellular pertussis (DTaP) vaccine. In total, 738 polymerase chain reaction–confirmed pertussis cases were diagnosed. Pertussis risk was 13 times higher among unvaccinated and nearly 2 times higher among undervaccinated children when compared with those who were fully vaccinated. However, >80% of the total pertussis cases were seen in children who had received all their recommended DTaP vaccine doses. Pertussis risk increased with increasing time since vaccination, clearly demonstrating waning immunity, which the KPNC group and others had previously reported.2,3 

Those individuals who began their medical career after 1997,...

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