Maternal Flu Vaccination Doesn't Impact Child's Autism Risk

One reason why some women refuse the influenza vaccine is because they believe that it increases the risk of autism spectrum disorders (ASDs). No scientific study has ever supported this belief, however, and the Centers for Disease Control and Prevention (CDC) strongly urges that everyone who meets the criteria gets vaccinated—including pregnant women.

Recent studies have found that maternal infection increases the risk of autism in offspring, but more data was needed on whether the flu is one of those infections. That’s where researchers from Kaiser Permanente Northern California come in.

The team collected data from 196,929 mother-baby pairs. All of the infants had a gestational age of at least 24 weeks and were born from 2000 to 2010 at the institution. The average woman’s age was around 31.

During pregnancy, 24,231 mothers (23%) received the influenza A (H1N1) vaccine—a subtype of the influenza A virus and the most common strain of flu in 2009. Out of the entire cohort, 1,400 mothers (0.7%) were diagnosed with the flu. A total of 3,101 babies (1.6%) were diagnosed with ASD.

Neither maternal flu infection or influenza vaccination were linked to an increased risk of ASD (hazard ratios: 1.04 and 1.10, respectively). This data includes getting vaccinated at any point during pregnancy and after adjusting for covariates.

“In trimester-specific analyses, first-trimester influenza vaccination was the only period associated with increased ASD risk (adjusted hazard ratio: 1.20),” the authors explained. “However, this association could be due to chance (P = 0.1) if Bonferroni corrected for multiplicity of hypotheses tested (n = 8).” In other words, these results were not statistically significant after adjusting for multiple comparisons. An increased risk was not observed in women who received the vaccine in their second or third trimester.

The researchers concluded that the results do not indicate a need to change vaccine practices in pregnant women. However, they do believe that more data is needed to better understand the relationship between maternal flu vaccination and autism.

ASDs were diagnosed based on the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes 299.0, 299.8, or 299.9.

The study, “Association Between Influenza Infection and Vaccination During Pregnancy and Risk of Autism Spectrum Disorder,” was published in JAMA Pediatrics. The news release was provided by The JAMA Network.

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