Vaccination During Pregnancy and Autism Risk

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RESEARCH UPDATE

Receiving the prenatal tetanus, diphtheria toxoid, and aceullar pertussis (Tdap) vaccine by the mother during pregnancy is not linked to increased autism spectrum disorder (ASD) risk in her infant, according to a large study.¹ It is the first to evaluate the risk of ASD in children exposed prenatally to the Tdap vaccine. The results support current CDC recommendations to vaccinate all pregnant women against Tdap.²

“We provide evidence supporting the ACIP’s recommendation to vaccinate pregnant women to protect vulnerable infants, who are at highest risk of hospitalization and death after pertussis infection,” wrote first author Tracy Becerra-Culqui, PhD, of Kaiser Permanente Southern California, Pasadena CA, and colleagues.
In recent years, pertussis (whooping cough) has been making a comeback in the US, due to waning immunity and suspicions about vaccination. Young infants are at highest risk of hospitalization and death from the highly contagious infection.

To protect infants, the CDC’s Advisory Committee on Immunization Practices (ACIP)²recommends that all pregnant women receive the Tdap vaccine regardless of past vaccination status. Studies suggests that maternal antibodies are passed through the placenta and are over 90% effective in providing immunity up to age 2, when most children receive their first dose of the Tdap vaccine.

Research has suggested that receiving the Tdap vaccine prenatally does not increase the risk of preterm delivery or low birth weight. But longer term outcomes such as ASD in the infant have not been evaluated.
To assess the issue, researchers conducted a retrospective cohort study that included mother-child pairs for infants born January 2011 through December 2014 at Kaiser Permanent Southern California hospitals. Data on prenatal Tdap vaccination and ASD diagnoses came from electronic medical records. The analysis included 81,993 children.

Key results

• 1.6% of children were diagnosed with ASD over a followup of 1.2 to 6.5 years
• No increased risk of ASD in Tdap exposed vs Tdap nonexposed children (unadjusted HR: 0.98, 95% CI 0.88-1.09)
• Results adjusted for 10 confounders and the probability of vaccination confirmed prenatal Tdap vaccination not linked to increased ASD risk in children (HR 0.85, 95% CI 0.77-0.95)

The authors mentioned several limitations. ASD diagnosis was determined by medical record data and not confirmed by study assessment. Also, the study included children diagnosed starting at age 1 year, but most children with ASD in the US are diagnosed between 3 to 5 years. So the study may have missed children with ASD, or those with milder ASD diagnosed when they reach school age.

Take home points

• Large retrospective study showed that Tdap vaccination during pregnancy is not linked to increased risk of ASD in offspring
• Results support CDC recommendations for Tdap vaccination of all pregnant women regardless of past vaccination status

References:

1. Becerra-Culqui TA, Getahun D, Chiu V, et al. Prenatal Tetanus, Diphtheria, Acellular Pertussis Vaccination and Autism Spectrum Disorder. Pediatrics. 2018 Sept.
2. Advisory Committee on Immunization Practices (ACIP). Updated Recommendations for Use of Tetanus Toxoid, Reduced Diphtheria Toxoid and Acellular Pertussis Vaccine (Tdap) in Pregnant Women and Persons Who Have or Anticipate Having Close Contact with an Infant Aged <12 Months --- Advisory Committee on Immunization Practices (ACIP), 2011. MMWR Morb Mortal Wkly Rep. 2011;60:1424–1426. https://www.cdc.gov/mmwr/preview/mmwrhtml/mm6041a4.htm. Accessed September 28, 2018.