During pregnancy, the developing fetus is vulnerable to the mother’s normal biological response to immune challenge. Recent epidemiological studies indicate that prenatal exposure to inflammatory signals from parasitic, bacterial and viral pathogens including the flu, shows significant correlations with neurological and immunological abnormalities, like autism spectrum disorder. Termed maternal immune activation (MIA), the role of inflammatory mediators during critical gestational periods has been shown to have adverse effects on fetal development.
There are many ways in which the maternal immune system can be activated. A study titled “Prenatal Fever and Autism Risk”supports the hypothesis that maternal fever in pregnancy, regardless of trimester and cause of the fever, is associated with increased risk of autism spectrum disorder (ASD) among offspring. While earlier studies found that prenatal exposure to infectious agents increased the risk of ASD in offspring, this study supports more recent findings that activation of the maternal immune system has deleterious effects on fetal brain development and plays a role in neurodevelopmental consequences. In this study, fever-associated ASD risk increased markedly with fever frequency particularly after 12 weeks gestation. Acetaminophen worked minimally to mitigate the risks for fevers occurring in the second trimester. Of the 538 cases, ASD was five times more prevalent in boys than girls. The authors’ findings support the hypothesis that in a subset of ASD cases, fever and associated immune disturbances may be implicated.
Vaccines are designed and intended to produce the same biological immune response as natural infection. When a person gets a vaccine, whether during pregnancy or at any other time, an immune response to that vaccine occurs.
Studies show that roughly 5% of the general population will acquire the influenza virus annually, however, if the influenza vaccine does its job, immune activation will occur in 100% of pregnant women who receive the flu shot.
Although the Zerbo et al. paper did not show a correlation between the actual flu in pregnancy and ASD, it did show women receiving the seasonal flu shot in the first trimester of pregnancy had 25% greater odds of having a child with ASD.