US Infant Pertussis Incidence Trends Before and After Implementation of the Maternal Tetanus, Diphtheria, and Pertussis Vaccine
Authors: Skoff Tami H. , Deng Li , Bozio Catherine H. , Hariri Susan 
Published: October 2023

ABSTRACT
Many illnesses can become especially serious when contracted within the first year of life; pertussis remains quite deadly despite recent medical advances in disease prevention. Current guidance on vaccination in the United States includes 3 doses of the DTaP (diphtheria, tetanus toxoid, and acellular pertussis) vaccine beginning at 2 months of age, but this regimen leaves infants younger than that very vulnerable to illness. Research has shown both that vaccinating mothers with tetanus toxoid reduces tetanus, diphtheria, and pertussis (Tdap) between 27 and 36 weeks of gestation significantly reduces instances of pertussis in infants younger than 2 months, and that maternal vaccination rates have risen in the last few years. However, research is lacking in analyzing the relationship between vaccination rates in pregnant mothers and the burden of pertussis in infants in the United States. This study was designed to assess data from 2000 to 2019 and examine the association of Tdap vaccination during pregnancy with trends in infant pertussis.
This analysis included data obtained from the National Notifiable Diseases Surveillance System between 2000 and 2019. This included a total of 57,460 cases of pertussis in infants younger than 1 year and a total of 19,322 cases in infants younger than 2 months. The rate of pertussis incidence for infants younger than 2 months in the time period before the implementation of prenatal Tdap was calculated to be 165.3 per 100,000 individuals, with no significant trend observed annually (P = 0.28). After the implementation of routine maternal Tdap, incidence decreased to 80.9 per 100,000 infants between 2017 and 2019. Accounting for both time periods, the mean annual incidence was calculated as 121.8 per 100,000 infants younger than 2 months. Annual incidence also showed a significant decreasing trend in the period after implementation of maternal Tdap vaccination (slope: −14.53 per 100,000 infants per year; P = 0.001). The change in trends before and after this implementation was also significant (P = 0.01).
In a slightly older age group of 6 to 12 months of age, mean annual incidence of pertussis was 19.7 per 100,000 infants. In the time period before implementation of maternal Tdap, incidence among infants aged 6 to 12 months was consistently 4 to 12 times less than infants younger than 2 months and did not significantly change after the implementation of the maternal vaccine. Comparing the 2 age groups, there was no significant change in the difference in incidence between infants younger than 2 months and those between 6 and 12 months in the period before the maternal vaccine, and after its implementation, there was a significant decrease in the incidence difference between the 2 groups (P < 0.001).
These results suggest an association between the maternal Tdap vaccination and trends of pertussis incidence in infants younger than 2 months. This also indicates a possible reduction in disease burden attributable to maternal Tdap vaccination before delivery. Limitations of this study include limited availability of individual maternal vaccination status, as well as an inability to identify if any infants were vaccinated before the age of 2 months. Further research should focus on clinical impact of the Tdap vaccination in context with the later DTaP vaccination and on analyzing the trends in disease associated with both vaccinations. Clinical guidelines should also be examined to ensure that public health trends and individual health trends are in alignment.