New research does not find an association between maternal flu infection and ASD.
Autism spectrum disorder (ASD) is an umbrella term covering autistic disorder, Asperger's syndrome, and pervasive developmental disorder.
ASD is reported to affect 1 in 68 children in the United States. Boys seem to be 4.5 times likelier to develop the disorder than girls.
The causes of ASD are currently unknown, although existing research points to genetic and environmental factors. Approximately 10 percent of children diagnosed with ASD also have Down syndrome or other genetic and chromosomal disorders.
ASD also tends to occur together with other non-ASD developmental disorders, the co-occurrence rate being 83 percent.
New research looks at the link between maternal influenza infection and vaccination during pregnancy and the risk of ASD development in offspring.
The link between ASD, flu, and flu vaccination
- ASD can be accurately diagnosed as early as 2 years of age
- Having older parents is a risk factor for developing ASD
- Almost half of the children diagnosed with ASD have average or above average intellectual ability.
The study - led by Ousseny Zerbo, Ph.D., of Kaiser Permanente Northern California in Oakland - examined 196,929 births over the course of a decade, from 2000-2010.
The results were published in JAMA Pediatrics.
The study sample included 1,400 mothers who had been diagnosed with influenza and 45,231 mothers who had received a flu vaccination during pregnancy.
Of all the births, 3,101 children, or 1.6 percent, were diagnosed with ASD.
The study did not find any association between a risk of ASD in offspring and influenza vaccination during pregnancy.
During the second and third trimesters of pregnancy, the researchers found no association, but the results suggested a very slight association between flu vaccination and ASD in the first trimester.
However, the authors emphasize that the association did not prove to be statistically significant after multiple adjustments, indicating that it was due to chance.
More research needed on first-trimester flu and ASD
Although the results do not suggest the need for any changes in policy or practice, the authors note that more studies on vaccination and pregnancy are needed.
The findings seem to confirm results from previous research Ousseny and team have carried out. Whereas their previous studies were limited in sample size, and the results may have suffered from recall bias, this new study compensated for the weaknesses by having a much larger sample size and using electronic medical records.
"We found no association between ASD risk and influenza infection during pregnancy or influenza vaccination during the second to third trimester of pregnancy. However, there was a suggestion of increased ASD risk among children whose mothers received influenza vaccinations early in pregnancy, although the association was insignificant after statistical correction for multiple comparisons.
While we do not advocate changes in vaccine policy or practice, we believe that additional studies are warranted to further evaluate any potential associations between first-trimester maternal influenza vaccination and autism."