A new study published in the Journal of the American Medical Association has found an increase in cases of autism for babies born to mothers who received a flu vaccination in the first trimester, yet headlines are reporting that no link was found.The study, Association Between Influenza Infection and Vaccination During Pregnancy and Risk of Autism Spectrum Disorder, was published on November 28 in JAMA. This large-scale study looked at the medical records of nearly 200,000 children born between 2000 and 2010 at Kaiser Permanente hospitals in Northern California.
Less than a quarter (23 percent) of the children's mothers received flu vaccines while they were pregnant. Of all of the mothers in the study (vaccinated and non-vaccinated), less than 1 percent were diagnosed with the flu while they were pregnant. The authors found no increased incidence of autism in the children of those mothers who contracted the flu during their pregnancy.
A total number of 3,101 (1.6 percent) of the children were eventually diagnosed with an autism spectrum disorder (ASD).
The study authors found that there was an increased incidence of ASD in children whose mothers received flu vaccines in the first trimester, although they said they could not be sure that it wasn't coincidence or caused by other factors.
"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)."
The researchers went on to say that they were able to get the numbers lower if they adjusted them in various ways, saying "this association could be due to chance" if they "corrected for the multiplicity of hypotheses tested."
They said that there was not an increased number of ASD cases in children of mothers who received flu vaccines later in pregnancy.
"Maternal influenza vaccination in the second or third trimester was not associated with increased ASD risk."
Despite this finding, news sources around the United States have been proclaiming that this study shows no increased risk of autism in children whose mothers received flu vaccines while pregnant.
"Flu or flu shot during pregnancy won't raise autism risk in child, study finds," proclaimed the Chicago Tribune.
"Study: Flu vaccine in pregnant women not linked to autism risk in children," said the American Academy of Pediatrics' News and Journals Gateway.
"Flu Vaccine During Pregnancy Not Linked To Autism," announced NPR.In every case, the fact that a correlation was found between autism and flu vaccination in the first trimester is buried much later in the article, and in some cases, the results are further muddied. The Chicago Tribune mentioned the correlation six paragraphs into their report, admitting that there was a "suggestion" of increased risk for autism in the child if the mother received a flu vaccination during her first trimester, but saying "this statistic disappeared after the researchers further refined their analysis" and that "this study was a retrospective look at data, so it can't prove or disprove any cause-and-effect relationships" about the higher incidence of ASD in those children.
At the very end of their story, the Chicago Tribune did say that one pediatrician said more research is needed regarding the higher ASD risk for babies born to mothers who received flu vaccines in their first trimester. They quoted Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Cohen Children's Medical Center in New Hyde Park, New York.
"Additional studies are needed to clarify whether or not there is an association between first-trimester influenza vaccinations and later autism spectrum disorders, so that more informed recommendations can be made to pregnant women."
AAP News and Journals Gateway, too, admitted the link between vaccination in the first trimester and higher rates of ASD diagnosis -- seven paragraphs down. They, too, mentioned the study author's concerns near the end of their story. In the eighth paragraph (out of 10 paragraphs total), they quoted the researchers about the need to study this correlation further.
"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."
In the case of NPR, the link between higher incidence of autism and flu vaccination in the first trimester was again buried late in the article. Here, it was mentioned in the sixth paragraph."But that could be due to chance, the researchers say," they wrote, "given the small numbers of children in that group and the multiple hypotheses the study tested."
NPR also mentioned towards the end of their story that the study did not look at whether the flu vaccines the mothers received contained thimerosal. They wrote that multidose containers of flu vaccine still contain thimerosal, a controversial preservative that contains small amounts of ethyl mercury. The FDA recommended that thimerosal should be removed from vaccines given to infants back in 1999 because of concerns about vaccine safety.
It is worth noting that only 23 percent of the mothers who took part in the study received a flu vaccine at any time during their pregnancies. The number of women receiving flu vaccines during pregnancy has been climbing steadily over recent years. UPI reports that data from the U.S. Centers for Disease Control and Prevention showed that half of pregnant women had received a flu shot in the 2015-2016 season.
Over the past 20 years, credible studies have shown a possible link between autism and vaccination -- and credible studies have shown the opposite. The science is far from proven on either side. That said, while the studies that claim to show no link get spread widely in the media, those that raise questions tend to be buried or criticized.
Among the reputable studies that showed possible links is a Utah State University study that found that "an inappropriate antibody response to MMR [vaccine], specifically the measles component thereof, might be related to pathogenesis of autism." Likewise, a five-year study of 79,000 children reported in the Journal of Toxicology and Environmental Health found that found boys given Hepatitis B vaccine at birth had a three times increased risk for autism than boys vaccinated later or not at all (nonwhite boys were at greatest risk).
A study on infant monkeys who were given the 1990s recommended pediatric vaccine regimen showed important brain changes warranting "additional research into the potential impact of an interaction between the MMR and thimerosal-containing vaccines on brain structure and function." Another study suggested "likely involvement" of thimerosal in vaccines (such as flu shots) "in neurodevelopmental disorders such as autism."
In addition, a study in the Journal of Child Neurology found a major flaw in a widely-cited study that claimed there was no link between thimerosal in vaccines and autism. The researchers wrote that "the original p value was in error and that a significant relation does exist between the blood levels of mercury and diagnosis of an autism spectrum disorder."
The researchers noted that, like the link between aspirin and heart attack, "even a small effect can have major health implications," and called on researchers to take a fresh look at that study.
"If there is any link between autism and mercury, it is absolutely crucial that the first reports of the question are not falsely stating that no link occurs."
Scientists in other countries have also published research on a possible link between vaccines and autism. One study from Japan's Kinki University supported "the possible biological plausibility for how low-dose exposure to mercury from thimerosal-containing vaccines may be associated with autism" and another from the University of British Columbia that found "the correlation between Aluminum in vaccines and [autism] may be causal."
These are just a few of the studies that have raised questions about a link between autism spectrum disorders and vaccines, though they are rarely reported in the press.
It is important to note that the latest study did not definitively prove anything for or against flu vaccine safety during pregnancy. The higher incidence of ASD diagnosis in children whose mothers received a flu vaccination during their first trimester was a relatively small difference -- but it was a difference that needs to be acknowledged and studied. It is also important to note that studies have linked many other factors to autism spectrum disorder, as well.
That said, if there is indeed a link between flu vaccination in the first trimester and autism spectrum disorders, burying legitimate scientific concerns under reassuring headlines is putting propaganda before children's health. This represents neither good science nor good reporting.
[Featured Image by Africa Studio/Shutterstock]