Antenatal tetanus, diphtheria, and acellular pertussis (Tdap) immunization and risk of serogroup 19 IPD in children: An indirect cohort study.

The tetanus-diphtheria-acellular pertussis (Tdap) vaccine has been indicated for pregnant women in Quebec, Canada since 2018. Recent literature suggests maternal Tdap interferes with the pneumococcal vaccine response in children exposed in utero because of maternally transferred anti-diphtheria antibodies, a phenomenon known as blunting. Using an indirect cohort study, we investigated whether maternal Tdap vaccination could alter the protection of PCV vaccines against serotype 19A/F IPD (conjugated to diphtheria toxoid in PCV10). Thirty-seven immunized IPD cases (serotype 19A/F) and 90 immunized IPD controls (non-vaccine serotypes) were analyzed using multivariate logistic regression. Our analyses did not identify antenatal Tdap exposure as a risk factor for IPD in vaccinated children, with and odds ratio close to the null (odds ratio = 0.82, 95%CI = 0.32-2.07). As this study is the first to assess the impact of maternal immunization on pneumococcal disease risk, future investigations involving a larger number of cases should be conducted to confirm or infirm our findings.