Abstract
Background
Maternal vaccination with the tetanus, diphtheria, and acellular pertussis vaccine during pregnancy is the most effective way to prevent pertussis in infants, especially in the first few months of life before infants are eligible to receive the diphtheria, tetanus, and acellular pertussis vaccine.
Objective
This study evaluated the effectiveness of 5-pertussis-component tetanus, diphtheria, and acellular pertussis (Tdap5) vaccination in pregnancy in protecting infants against pertussis disease during the first 2 and 12 months of life.
Study design
This was a retrospective observational study that included all full-term infants born at Kaiser Permanente Northern California hospitals between January 1, 2010 and December 31, 2019. We used Cox regression models to estimate the adjusted hazard ratio of the risk of pertussis in infants in the first 2 months and 12 months of life, comparing infants of vaccinated and unvaccinated women with Tdap5 during pregnancy. Each Cox model was specified on a calendar timeline and stratified by infant’s month and year of birth and was adjusted for sex, race, delivery hospital, and maternal Tdap5 vaccination status before and after pregnancy. We calculated vaccine effectiveness as 1 minus adjusted hazard ratio, expressed as a percentage, which estimated the percent reduction in the incidence of infant pertussis.
Results
There were 263,809 infants in the study, 64.7% (n=170,799) of whom were born to women vaccinated with Tdap5 during pregnancy. During the first 2 months of life, pertussis incidence was 3.5 per 100,000 person-years among infants of Tdap5-vaccinated women vs 114.6 per 100,000 person-years among infants of unvaccinated women. During the first 12 months of life, pertussis incidence was 27.8 per 100,000 person-years among infants of vaccinated women vs 110.4 per 100,000 person-years among infants of unvaccinated women. Compared with infants of unvaccinated women, the effectiveness of Tdap5 vaccination in pregnancy was 96.0% (95% confidence interval, 64.6, 99.6; P=.004) against pertussis during the first 2 months of life and 55.8% (95% confidence interval, 27.1, 73.2; P=.001) against pertussis during the first year of life.
Conclusion
Maternal Tdap5 vaccination during pregnancy was highly effective in protecting infants against pertussis before they have protection from diphtheria, tetanus, and acellular pertussis. Tdap5 vaccination during pregnancy continued to provide additional protection for infants through the first year of life beyond the protection they receive from diphtheria, tetanus, and acellular pertussis.