Maternal immunization with the tetanus, diphtheria, and acellular pertussis (Tdap) vaccine was not associated with increased risk of adverse health outcomes in offspring up to age 6 years, supporting the long-term safety of Tdap administration in pregnancy, according to data from a population-based retrospective cohort study published in Pediatrics.1

“The highest burden of pertussis infection and mortality, even in highly vaccinated populations such as the United States, is among young infants,” senior author of the study Deshayne B. Fell, PhD, said. Infants are eligible to receive their first DTaP dose at 2 months of age and aren’t fully protected until about 6 months of age, explained Dr. Fell, who is associate professor in the School of Epidemiology and Public Health at the University of Ottawa and scientist at the Children’s Hospital of Eastern Ontario (CHEO) Research Institute, both in Ontario, Canada.

“This leaves infants completely unprotected before 2 months of age or only partly protected against pertussis after 2 months of age but before completion of their vaccine series,” Dr. Fell said. “Maternal immunization with Tdap vaccine during pregnancy transfers maternal antibodies to the babies before they are born, which protects them from pertussis infection during those early months. This has been shown to be highly effective in numerous studies.”


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However, few studies have assessed the potential for long-term adverse health effects of maternal immunization with Tdap on children, the authors noted.

Population-Based Cohort Study

To assess the long-term safety of Tdap exposure during pregnancy, Meghan Laverty, MSc, of the University of Ottawa, and colleagues used multiple linked province-wide health administrative databases to assess outcomes in all live births between April 2012 and March 2017 (N=625,643) in Ontario. Of this cohort, 12,045 children who were exposed to Tdap in utero were matched to 60,225 unexposed infants. The children were followed for up to 6 years

The researchers found no significant association between prenatal Tdap exposure and increased risk of any of the following prespecified adverse childhood outcomes:

  • Immune-related outcomes: infections (upper and lower respiratory infections, gastrointestinal infections, and otitis media) and asthma
  • Nonimmune-related outcomes: sensory disorders (hearing loss and vision loss) and neoplasm
  • Nonspecific outcomes: urgent and inpatient health service use

In contrast, Tdap exposure was linked to a reduced risk of upper respiratory infections, gastrointestinal infections, and urgent and inpatient health service use (Table).

Table. Association Between Tdap Exposure in Pregnancy and Pediatric Health Outcomes1

OutcomeAdjusted Estimate From Matched Sample (95% CI)
Asthmaa0.93 (0.82–1.04)
Infectious disease  
Upper respiratory infections  
Lower respiratory infections  
Gastrointestinal infections  
Otitis media

0.94 (0.90–0.99)
0.94 (0.88–1.00)
0.85 (0.79–0.91)
0.97 (0.91–1.04)
Neoplasm1.36 (0.76–2.44)
Sensory disorders0.72 (0.34–1.52)
Urgent/inpatient health service use0.93 (0.91–0.96)
aCohort for asthma was restricted to children with a minimum 3-year follow-up

Limitations of the study include the inability to rule out the effects of possible unmeasured confounding factors linked to a higher or lower risk of adverse outcomes in the exposed or unexposed groups. Other limitations include possible nondifferential exposure or outcome misclassification, and the low number of neoplasms in the Tdap-exposed group.

Will COVID-19 Affect Pertussis Rates in Infants?

Despite the known benefits of maternal pertussis immunization on protecting newborns, a large proportion of women in the US (45%) do not receive a pertussis-containing vaccine during pregnancy, according to data from the Centers Disease Control and Prevention.2 Black, non-Hispanic women had lower vaccination rates than women of other races and were less likely to report a health care provider offer or referral for vaccination.

“There is a concern that routine infant immunization programs may not be reaching infants in a timely manner, leaving some infants unprotected against pertussis as well as other dangerous vaccine-preventable infections,” Dr. Fells said. “Although the lockdowns and other public health measures during the COVID-19 pandemic seem to have decreased rates of some types of infections (eg, influenza), as things start to open up, we don’t want to have a cohort of young infants who are susceptible to vaccine-preventable diseases such as pertussis, measles, or mumps.”

Thus, “it is still really important to maintain the routine childhood immunization schedule as closely as possible and maternal immunization programs for influenza and pertussis are important for the same reason,” Dr. Fell said. “Even if there is a decline in some areas in the incidence of influenza and pertussis, we know these types of infections will return especially as public health measures are relaxed. Again, maternal immunization is primarily protecting infants in a time period when they are not yet protected by their own vaccination series and continues to be important.”

Some authors have declared affiliations with or received funding from the pharmaceutical industry. Please refer to the original study for a full list of disclosures.

References

1. Laverty M, Crowcroft N, Bolotin S, et al. Health Outcomes in young children following pertussis vaccination during pregnancy. Pediatrics. 2021 Apr 19:e2020042507. doi:10.1542/peds.2020-042507.

2. Low rates of vaccination during pregnancy leave moms, babies unprotected. News release. Centers for Disease Control and Prevention. October 7, 2019. Accessed April 21, 2021. https://www.cdc.gov/media/releases/2019/p1008-vaccination-moms-babies-unprotected.html