Does prenatal Tdap vaccination increase autism risk for infants?

Ever since Andrew Wakefield, MD, penned a now-disproven report on a link between measles/mumps/rubella (MMR) vaccines and autism in the 1990s, clinicians and researchers have worked to prove the safety and necessity of recommended vaccinations. Now, a new report offers proof that there also is no connection between prenatal maternal tetanus/diphtheria/acellular pertussis (Tdap) vaccination and autism spectrum disorders (ASD) n offspring.

The study, published in Pediatrics, specifically reviewed the safety of the Tdap vaccine in light of recent recommendations that it be given to pregnant women to offer protection against these diseases in infants.¹ Neonates can’t receive the vaccine at birth, and recent studies have shown a 46% reduction in pertussis cases and a 75% reduction in pertussis hospitalizations in newborns as a result of prenatal Tdap vaccination.

Pertussis is a highly contagious infection-especially dangerous for infants-and prevalence of cases alongside waning immunity has been increasing in recent years. Additionally, infants can’t be immunized against pertussis until aged 2 months, which leaves them susceptible to infection. The Centers for Disease Control and Prevention (CDC) began recommending prenatal vaccination in 2013 in the hope that mothers will pass antibodies on to their newborns, and now the evidence is available to prove the efficacy of administration during late pregnancy.

Tdap and autism

This new study, however, sought to assess whether there was a link between prenatal Tdap vaccination and development of ASD. Researchers studied more than 109,000 mothers at Kaiser Permanente Southern California hospitals between 2011 and 2014. The children of the vaccinated mothers were followed for several years, and ASD was diagnosed in 1.6% of the children of mothers vaccinated during their pregnancies.

The report reveals that the incidence of autism diagnoses declined throughout the study period, from 2% to 1.5% in children of mothers who were not vaccinated during pregnancy, and from 1.8% to 1.2% in mothers who did receive the vaccination. Overall, researchers note, the incidence of ASD in the vaccinated group was 3.78 per 1000 person-years compared with 4.05 per 1000 person-years in the unvaccinated group.

“We found no evidence of increased risk for ASD diagnosis associated with Tdap vaccination during pregnancy,” the report concludes.

The research team notes than in addition to finding no link between prenatal Tdap vaccination and ASD risk, prenatal vaccination also may offer protections against infections that could otherwise lead to neurodevelopmental problems.

Researchers state that whereas vaccinations in pregnancy may also activate the maternal immune system and lead to “neurodevelopmental insults,” there was insufficient data to support this hypothesis in the research included in this retrospective study.

The study team concludes that the recommendation for prenatal Tdap vaccination by the CDC’s Advisory Committee on Immunization Practices (ACIP) is warranted and suggests that future studies could include a longer surveillance period of infants of vaccinated mothers.