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A recent study has shown that no association exists between pregnant women infected with influenza, or receiving an influenza vaccine, and the development of autism in their babies during the second and third trimesters of pregnancy.

It is known that fever and maternal infections during pregnancy are associated with an elevated risk for the development of autism spectrum disorders (ASDs). There has, however, been no study to investigate whether an association exists between receiving the influenza vaccine during pregnancy and babies of these pregnant women developing autism spectrum disorders. The objective of the study, that will be discussed, was to then determine whether such risk existed.

The study

Researchers at Kaiser Permanente Northern California in Oakland, California collected and analyzed data from nearly 197,000 children born between 2000 and 2010, and who were at least 24 weeks gestational age during their mothers' pregnancies. This information included the prevalence of maternal influenza infection, as defined by clinical diagnostic codes or positive laboratory results, and influenza vaccinations given to pregnant women recorded from conception date to delivery date. 

This information was then compared to the clinical diagnoses of children with ASDs, born from the above-mentioned mothers, identified by clinical diagnostic codes on at least 2 occasions any time from their births until June 2015.

The findings

When all the data was captured and analyzed, the following findings were made:

  • 1,400 mothers (0.7% of the sample size) were diagnosed with influenza and over 45,000 mothers (nearly 23%) had received the influenza vaccine during pregnancy.
  • Over 3,100 children were diagnosed with ASD.
  • It was determined that maternal influenza infection or influenza vaccination administered at anytime during pregnancy was not associated with an increased risk of children developing ASD. 
  • Regarding trimester-specific findings, influenza vaccine given during the first trimester of pregnancy was the only period associated with an increased risk of children developing ASD. A special note was made though that this association could be due to chance and was therefore not statistically significant.

There were a few limitations to this study as well as the fact that causality of ASD, due to maternal infections and exposure to flu vaccines, couldn't be established. 

The clinical significance

The researchers of this study suggest that since no association exists between maternal infections or the use of flu vaccines in pregnancy and the development of autism spectrum disorders in children born from these mothers, then there should be no changes in vaccine policy or practice.

Health care professionals can use this information to put mothers minds at ease when it comes to worrying about whether autism in their children has anything to do with flu vaccine exposure when they were pregnant with their children. 

Further research

The researchers have also stated that the issue of the increased risk of developing ASD due to administration of the flu vaccine in the first trimester of pregnancy, which was attributed to chance, warrants further clinical studies to investigate and evaluate whether there are any potential associations between these aspects.

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