SciCheck Digest
COVID-19 vaccination during pregnancy benefits both mother and baby. Side effects are generally mild, and studies don’t show negative effects on the baby. A criticized study that gave COVID-19 vaccines to pregnant rats doesn’t show that vaccines cause autism or that people shouldn’t get COVID-19 vaccines, contrary to claims.
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COVID-19 vaccination protects pregnant people from severe COVID-19 and reduces COVID-19 risks for babies. As is the case in people who aren’t pregnant, side effects in pregnant people are usually mild and resolve within days. Studies do not show a link between COVID-19 vaccination and negative pregnancy outcomes or health problems for babies.
Long-standing claims that childhood vaccines cause autism have been roundly debunked. Long-term studies provide reassurance that vaccination during pregnancy against flu and other diseases does not increase a child’s risk of autism, a developmental disorder. And a recent study did not find a connection between maternal COVID-19 vaccination and increased risk of developmental delay at 18 months of age.
However, social media posts have misused findings from a recent study of COVID-19-vaccinated pregnant rats and their pups to back up unfounded claims that people should not take COVID-19 vaccines, or to promote unsubstantiated claims about vaccines and autism.
“I’m forever grateful I risked my reputation in my personal life to warn people far and wide to NOT get this experimental $h0t!” said one post sharing an article from the Epoch Times on the new study.
Commentator Candace Owens, who has a history of spreading misinformation, shared a post about the study on X, the platform formerly known as Twitter, saying it supported long-standing, debunked claims about vaccines and autism. “That’s because vaccines and autism have always been linked, which affected mothers have been trying to tell the general public for decades,” she said. Posts about the study have continued to spread.
Researchers who study brain development expressed concerns to us about how the rat study was designed and interpreted.
The authors of the study, published Jan. 10 in Neurochemical Research, did behavioral and other tests on rats born to 15 female rats impregnated by five males. The pregnant rats either received an adult human-sized dose of the Pfizer/BioNTech vaccine against COVID-19 or a saline injection.
The researchers wrote that they observed “autism-like behaviors,” such as decreased interactions with an unfamiliar rat, and decreased neurons in regions of the brain in male rats born to vaccinated mothers. They also said they found alterations in the level of a particular protein in the brains of rats of both sexes born to vaccinated mothers.
Even if the results are taken at face value, it’s not possible to conclude from a study in rats that vaccines cause autism, because rat and human biology and behavior are different. Researchers do study rats to better understand autism, but these studies are meant to generate hypotheses, not change medical care.
Experts also told us there were various factors that made the study hard to interpret, such as the high vaccine dose given to the pregnant rats, despite their small size, the lack of replication of the experiment and issues with the statistical analyses.
“Caution should be exercised in generalizing these results to humans,” the authors themselves wrote in the paper. Corresponding author Mumin Alper Erdogan, a professor in the department of physiology at Izmir Katip Celebi University in Turkey, did not respond to a request for comment from us. However, he did answer questions from Health Feedback, responding to some criticisms and clarifying that there was “no intention, desire, or effort on our part to oppose vaccinations or make similar accusations.”
“Vaccines do not cause autism,” a spokesperson from the Centers for Disease Control and Prevention told us in an email. “To date, no vaccine safety monitoring data in the United States indicates a causal association between autism and COVID-19 vaccination.”
Rat Study Provides Limited Information
Multiple scientists expressed concerns to us about the high COVID-19 vaccine dose given to the pregnant rats.
Staci Bilbo, a neuroimmunologist at Duke University who studies how the immune system influences brain development, told us that vaccine doses are “extremely carefully” adjusted during vaccine development. Researchers determine the smallest dose that will generate the needed immune response.
Giving the rats — which on average weighed less than 8 ounces — a full adult human COVID-19 vaccine dose was equivalent to giving an average-weight American woman around 350 times the recommended dose of the Pfizer/BioNTech vaccine, according to Bilbo’s calculation.
“If you give a high enough dose of anything it’s going to probably have impacts,” she said.
In response to questions about the dose, Erdogan told Health Feedback that “there’s no established standard for mRNA vaccine dosages in rats due to the lack of specific dose studies” and that relatively high doses have been used for studies of other animals of varying sizes.
Jeffrey S. Morris, director of the division of biostatistics at the University of Pennsylvania’s Perelman School of Medicine, also told FactCheck.org that the high dose given to the rats was a limitation of the study. “This does not make the results irrelevant, since super high dose can potentially detect some potential issue that might manifest in some humans, but if I were reviewing this article I would make the authors emphasize the multiple of how much larger the effective dose in the animal study is to the current human dose, and include the qualifier that this is one reason why it is not clear whether these results are relevant to what is experienced by humans given the current doses.”
Christopher Coe, a psychoneuroimmunologist and professor emeritus at the University of Wisconsin-Madison, told us via email that were it his study, he would also have wanted to give the rats a low dose of the vaccine to see if results varied by dose. Coe has done studies on the effects of infection and maternal inflammation on the fetus during pregnancy.
Coe said it was important to take reports of drug or vaccine adverse events seriously, but he also listed numerous other concerns about the paper.
For example, he said the researchers did not provide information about the rats and their pregnancies that could have shed light on how the injections affected them — and whether or not this was likely to be relevant to humans. This missing information included, for instance, whether the rats had an inflammatory reaction to the injections — the hypothesized pathway for how vaccination during pregnancy might affect neurodevelopment.
Teresa Reyes, a professor of pharmacology and systems physiology at the University of Cincinnati College of Medicine, told us via email that information was missing on the length of the rat pregnancies. “If the pregnancy length was significantly different, it could indicate that the litters were born prematurely, which confounds the interpretation of the findings,” she said.
In humans, COVID-19 vaccination during pregnancy has not been shown to increase preterm birth and may even protect against it.
She also said that information was missing on the weights of the pregnant rats, or dams, over time and their pups. “Significant differences in weight (e.g., vaccine exposed dams lost weight during the study) could indicate that the dams were severely ill in response to the vaccine, again confounding the interpretation of the study,” she said.
Coe said that he would have wanted “to replicate the findings rather than rush to publish on the basis of one experiment,” suggesting that both the authors of the paper and outside researchers should try to replicate the results.
And he expressed concern about the study’s statements that altered rat behaviors were “autism-like,” given that autism spectrum disorder is a “complex neurodevelopmental disorder.”
Brian Lee, an associate professor of epidemiology and biostatistics at the Drexel University Dornsife School of Public Health who studies prenatal exposures and autism risk, told us via email that it is hard to diagnose autism in humans, let alone in rats. “It’s hard to read into some behavioral tests for a rat and imagine it translates 100% to an autism diagnosis in humans,” he said.
There also appeared to be issues with the study’s experimental design and statistical analysis.
For instance, studies of prenatal exposures need to account for something called “litter effects” — or the fact that the multiple offspring born in the same litter to the same animal mother might share characteristics.
“The authors did not describe any approach to address the potential for a litter confound which could skew the findings (e.g., one dam has a significantly different response, multiple pups are used from that litter, and this skews the findings),” Reyes said.
Additionally, the authors wrote that they set out to determine whether maternal vaccination led to “any sex-specific neurobehavioral changes” — or ways in which sex and vaccination, in combination, affected the rats’ behavior.
The authors didn’t find evidence of such sex-specific effects on social behavior, but they nevertheless went on to compare social behavioral results from the male pups of vaccinated mothers versus unvaccinated mothers and highlighted the results — something Reyes said they shouldn’t have done. “By improperly using statistics to analyze the data, the conclusions are not valid,” she said. “It is impossible to verify the stated claims because statistics were used incorrectly.”
Evidence Indicates Maternal Vaccination Is Effective, Safe
A person’s likelihood of being autistic is influenced by a combination of genetics and other factors. These likely include older parental age and whether there are complications at a child’s birth, including extreme prematurity or very low birth weight. As we’ve written previously, many lines of evidence contradict the idea — long spread by anti-vaccine groups — that childhood vaccines cause autism.
Some theoretical concerns about vaccines given during pregnancy and autism are based on research indicating that infections during pregnancy might slightly increase the risk of a child later developing autism. “We know that immune activation can impact the way the brain develops, and sometimes that’s in adverse ways and yet we also know that the immune system is important in just normal brain development,” Bilbo said.
But Bilbo said the body’s immune system reacts differently to a serious infection than it does to vaccination. A vaccine against a virus is designed to expose the body to just enough viral material to teach the immune system to recognize the infectious agent, should it encounter it later. “Dose matters, obviously,” Bilbo said. “It matters quite a bit.”
Studies in humans provide reassurance of recommended vaccines’ benefits and safety.
The Tdap vaccine — which protects against tetanus, diphtheria and pertussis, or whooping cough — is recommended during pregnancy to protect newborns until they are able to be vaccinated against pertussis themselves at two months of age. The CDC began to recommend the vaccine routinely in all pregnancies in 2012, based on an uptick in pertussis, which can lead to death in very young babies.
A 2018 study of children born in Kaiser Permanente Southern California hospitals between 2011 and 2014 found no increased risk of autism in those whose mothers had been vaccinated against Tdap during pregnancy.
Flu vaccines have long been recommended for pregnant people during flu season and reduce risks for both the mother and the baby. A 2020 Swedish study looking at vaccination against the 2009 pandemic swine flu found no link between vaccination during pregnancy and increased autism risk.
A 2017 study, looking at children born in the Kaiser Permanente Northern California health system between 2000 and 2010, found no association overall between autism and flu vaccination during pregnancy. The researchers did find a “suggestion” of increased autism risk when mothers were vaccinated during the first trimester of pregnancy but said that statistical analyses indicated the “finding could be due to chance.”
In the case of COVID-19 vaccines, research has not indicated any negative impacts on pregnancy outcomes or on babies of vaccinated mothers. In fact, there’s some evidence maternal vaccination is protective against certain bad pregnancy outcomes, such as preterm birth and stillbirth.
A study published on Jan. 22 in JAMA Pediatrics followed around 4,200 children born to mothers who enrolled in the study between May 2020 and August 2021. At 18 months, scores on a developmental screening test did not differ between children whose mothers got COVID-19 vaccines during pregnancy versus those whose mothers didn’t.
The authors wrote that “these data suggest that maternal vaccination against COVID-19 during pregnancy was safe from the perspective of offspring neurodevelopment through 18 months of age.”
“It’s small and just 1 study, and of course more study is needed, but the findings are reassuring,” said Drexel’s Lee, who was not involved in the new study.
Coe emphasized the benefits of COVID-19 vaccination during pregnancy. “There are now many clinical studies that have demonstrated the benefits for safer pregnancy outcomes (as compared to the risk of an actual infection), as well as the reduced risk for young infants of getting a respiratory infection during the first 6 months of life,” he said.
“There is no known link between COVID-19 vaccines and the occurrence of autism spectrum disorder (ASD),” a Pfizer spokesperson told us in an email. “With hundreds of millions of doses of COVID-19 vaccines from BioNTech and Pfizer administered globally, the benefit-risk profile of our vaccines remains positive for all authorized indications/uses and age groups.”
Editor’s note: SciCheck’s articles providing accurate health information and correcting health misinformation are made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over FactCheck.org’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation.
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