The introduction of maternal tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccination was found to provide a sustained decrease in pertussis incidence among infants younger than 2 months, according to study results published in JAMA Pediatrics.
Researchers conducted an ecologic, time-trend analysis between January 2000 and December 2019 using data sourced from the National Notifiable Diseases Surveillance System on pertussis incidence among infants. Pertussis incidence rates were evaluated in the pre- (2000-210) and post- (2012-2019) maternal Tdap vaccination periods and compared between infants in target (<2 months) vs comparison (6 ≤12 months) groups. Segmented linear regression assuming a Poisson distribution was used to determine pertussis incidence rates for each group in both vaccination periods. The slope of the regression line was used to indicate trends in pertussis incidence.
A total of 57,460 infants younger than 12 months had pertussis between 2000 and 2019, of whom 19,322 (33.6%) were younger than 2 months. In the pre-maternal Tdap period, annual pertussis incidence did not significantly differ between infants in the target vs comparison groups. The mean annual incidence of pertussis in among infants in the target group was 165.3 per 100,000 infants, with a regression line slope of 3.29 per 100,000 infants (P =.28). For infants in the comparison group, the mean annual incidence was 19.7 per 100,000 infants, with a slope of 2.10 per 100,000 infants (P =.01).
In the post-maternal Tdap period, a significant decrease in mean annual pertussis incidence per 100,000 infants was observed among those in the target group (121.8; slope, -14.53; P =.001). However, mean annual pertussis incidence rates among infants in the comparison group did not significantly differ between the pre- and post-maternal Tdap vaccination periods (slope, 1.42 per 100,000 infants; P =.29).
In the pre-maternal Tdap vaccination period, pertussis incidence rates were not significantly different between infants in the target and comparison groups (slope, 0.08 per 100,000 infants per year; P =.97). In the post-maternal Tdap vaccination period, a significant decrease in the incidence rate difference between the groups was observed (slope, -14.43 per 100,000 infants per year; P <.001).
An overall difference between annual incidence rate differences of -14.51 per 100,000 infants was observed in the pre- vs post-maternal Tdap vaccination periods (P =.01), indicating vaccine uptake was associated with pertussis trends in infants younger than 2 months.
Limitations include the inability to identify individual maternal Tdap vaccination status.
According to the researchers, “Additional increases in the uptake of Tdap vaccination during pregnancy may be associated with further decreases in the incidence of pertussis among infants younger than 2 months.”
Skoff TH, Deng L, Bozio CH, Hariri S. US infant pertussis incidence trends before and after implementation of the maternal tetanus, diphtheria, and pertussis vaccine. Published online February 6, 2023. JAMA Pediatr. doi:10.1001/jamapediatrics.2022.5689