One reason why some people 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.
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Ousseny Zerbo, Yinge
Qian, Cathleen Yoshida, et al. Association
Between Influenza Infection and Vaccination During Pregnancy and Risk of Autism
Spectrum Disorder. JAMA Pediatr.
Published online November 28, 2016. doi:10.1001/jamapediatrics.2016.3609
Key Points
Question Is there an
association between maternal influenza infection and vaccination and autism
risk?
Findings In a cohort
study of 196 929 children, of whom 3103 had austism spectrum disorder, maternal
influenza infection during pregnancy was not associated with increased autism
risk. There was a suggestion of increased risk of autism spectrum disorders
among children whose mothers received an influenza vaccination during their
first trimester, but the association was statistically insignificant after
adjusting for multiple comparisons, indicating that the finding could be due to
chance.
Meaning Our findings
do not call for vaccine policy or practice changes but do suggest the need for
additional studies.
Abstract
Importance Maternal
infections and fever during pregnancy are associated with increased risk for
autism spectrum disorders (ASDs). To our knowledge, no study has investigated
the association between influenza vaccination during pregnancy and ASD.
Objective To
investigate the association between influenza infection and vaccination during
pregnancy and ASD risk.
Design, Setting, and Participants This cohort study included 196 929 children
born at Kaiser Permanente Northern California from January 1, 2000 to December
31, 2010, at a gestational age of at least 24 weeks.
Exposures Data on
maternal influenza infection and vaccination from conception date to delivery date,
obtained from Kaiser Permanente Northern California inpatient and outpatient
databases. Influenza infection was defined by the International Classification
of Diseases, Ninth Revision, Clinical Modification codes or positive influenza
laboratory test results.
Main Outcomes and Measures
Clinical diagnoses of ASDs identified by International Classification of
Diseases, Ninth Revision, Clinical Modification codes 299.0, 299.8, or 299.9
recorded in Kaiser Permanente Northern California electronic medical records on
at least 2 occasions any time from birth through June 2015.
Results Within this
cohort of 196 929 children, influenza was diagnosed in 1400 (0.7%) mothers and
45 231 (23%) received an influenza vaccination during pregnancy. The mean (SD)
ages of vaccinated and unvaccinated women were 31.6 (5.2) and 30.4 (5.6) years,
respectively. A total number of 3101 (1.6%) children were diagnosed with ASD.
After adjusting for covariates, we found that maternal influenza infection
(adjusted hazard ratio, 1.04; 95% CI, 0.68-1.58) or influenza vaccination
(adjusted hazard ratio, 1.10; 95% CI, 1.00-1.21) anytime during pregnancy was
not associated with increased ASD risk. In trimester-specific analyses,
first-trimester influenza vaccination was the only period associated with
increased ASD risk (adjusted hazard ratio, 1.20; 95% CI, 1.04-1.39). However,
this association could be due to chance (P = 0.1) if Bonferroni corrected for
the multiplicity of hypotheses tested (n = 8). Maternal influenza vaccination
in the second or third trimester was not associated with increased ASD risk.
Conclusions and Relevance
There was no association between maternal influenza infection anytime
during pregnancy and increased ASD risk. There was a suggestion of increased
ASD risk among children whose mothers received an influenza vaccination in
their first trimester, but the association was not statistically significant
after adjusting for multiple comparisons, indicating that the finding could be
due to chance. These findings do not call for changes in vaccine policy or
practice, but do suggest the need for additional studies on maternal influenza
vaccination and autism.
Jiang HY, Xu LL, Shao L, Xia RM, Yu ZH, Ling ZX, Yang F, Deng M, Ruan B. Maternal infection during pregnancy and risk of autism spectrum disorders: A systematic review and meta-analysis. Brain Behav Immun. 2016 Nov;58:165-172.
ReplyDeleteAbstract
Conflicting evidence exists with regard to the relationship between maternal infection during pregnancy and the risk of autism spectrum disorder (ASD) in offspring. The aim of this meta-analysis was to systematically assess this relationship. To identify relevant studies, we conducted systematic searches in PubMed and Embase of scientific articles published through March 2016. Random-effects models were adopted to estimate overall relative risk. A total of 15 studies (2 cohort and 13 case-control studies) involving more than 40,000 ASD cases were included in our meta-analysis. Our results showed that maternal infection during pregnancy was associated with an increased risk of ASD in offspring (OR=1.13, 95% confidence interval (CI): 1.03-1.23), particularly among those requiring hospitalization (OR=1.30, 95% CI: 1.14-1.50). Subgroup analyses suggested that risk may be modulated by the type of infectious agent, time of infectious exposure, and site of infection. These findings indicate that maternal infection during pregnancy increases the risk of ASD in offspring. Possible mechanisms may include direct effects of pathogens and, more indirectly, the effects of inflammatory responses on the developing brain.