SciCheck Digest

Being vaccinated against COVID-19 helps protect pregnant people from severe COVID-19. When given during pregnancy, the vaccines can also reduce the risk of hospitalization from COVID-19 early in a baby’s life. A new study adds to the evidence that vaccination during pregnancy is safe for babies, contrary to social media and online claims.

Pregnancy puts people at elevated risk of severe COVID-19. Young babies also are particularly vulnerable to hospitalization from COVID-19. Maternal vaccination reduces these risks.

The mRNA COVID-19 vaccines come with similar side effects regardless of whether a person is pregnant. Research does not show increased risk of miscarriage, birth defects or other pregnancy complications after vaccination, and it indicates vaccination may reduce the risk of preterm birth and stillbirth. A study published Oct. 23 in JAMA Pediatrics adds to the evidence that the mRNA COVID-19 vaccines are safe and do not lead to problems for newborn babies and infants when given to their mothers during pregnancy.

Going against the now-extensive record on COVID-19 vaccines and pregnancy, a recent Instagram post claimed that there is “No Discernable Benefit of COVID-19 Vaccination in Pregnancy.” The post was quoting a Substack newsletter from Dr. Peter McCullough, a prolific spreader of vaccine misinformation. The newsletter focused on the new JAMA Pediatrics study on vaccine safety, also claiming that it found “No Assurances on Safety.”

“Surely there was no benefit of COVID-19 vaccination, so why expose mothers and infants to any risk at all?” the newsletter misleadingly concluded. We reached out to McCullough with questions but did not receive a response.

This contradicts the conclusions of the authors of the paper, who wrote, “Maternal mRNA COVID-19 vaccination during pregnancy was not associated with increased adverse newborn and early infant outcomes and may be protective against adverse newborn outcomes.”

The study was a safety study and was not meant to assess vaccine effectiveness in pregnant women, co-author Sarah C. J. Jorgensen, a pharmacist and postdoctoral fellow at the University of Toronto, told us. The researchers aimed to measure whether the babies of mothers vaccinated during pregnancy had any elevated risks of health problems. Jorgensen said the study “does provide more reassuring data on the safety of these vaccines for the newborns and infants.”

The Centers for Disease Control and Prevention recommends that people 6 months and older, including people who are pregnant, receive an updated COVID-19 vaccine. Other medical organizations, including the American College of Obstetricians and Gynecologists and the Society for Maternal-Fetal Medicine, endorse this recommendation.

Study Bolsters Evidence for Safety of Maternal COVID-19 Vaccines

McCullough misused two pieces of raw data from the JAMA Pediatrics study to incorrectly imply that COVID-19 vaccination during pregnancy is unsafe and ineffective. He ignored the primary results of the paper supporting the safety of maternal COVID-19 vaccination for babies, as well as the larger body of data showing maternal COVID-19 vaccination is safe and effective.

The study used a database, called MOMBABY, that links health records of mothers and babies born in hospitals in Ontario, Canada. Jorgensen and her co-authors based their findings on data from more than 142,000 babies with due dates between May 2021 and early September 2022.

The researchers compared babies born to mothers who received at least one mRNA COVID-19 vaccine dose during pregnancy with babies whose mothers had never been vaccinated against COVID-19 at all prior to giving birth.

McCullough misleadingly referenced unadjusted, or “crude,” data suggesting a very small increased risk of hospital readmission for all causes in newborns up to 4 weeks old born to vaccinated mothers. But the correct statistic to use to determine whether there is a difference in readmissions is the adjusted figure, Victoria Male, a senior lecturer in reproductive immunology at Imperial College London, told us via email. Male was not involved in the study.

There are many differences between people who do or do not take COVID-19 vaccines. Well-done studies track characteristics of people in the groups they are comparing so they can adjust for differences, such as whether they live in high-income areas or have a tendency to engage in healthy behaviors.

“The adjusted results, after accounting for differences in the characteristics of the different groups, show no increased risk for neonatal readmission between the two groups,” pediatrics and internal medicine specialist Dr. Malini DeSilva and statistician Gabriela Vazquez-Benitez told us in an email. Both researchers, who were not involved in the study, are affiliated with HealthPartners Institute and study vaccine safety in pregnant people.

DeSilva and Vazquez-Benitez added that the study did not show an increased risk for neonatal readmission with additional COVID-19 vaccine doses received during pregnancy. The study also followed babies through 6 months of age and found a similar rate of hospital readmission regardless of maternal vaccination status.

Jorgensen and her co-authors wrote that the slight increased risk of newborn readmission in the crude data could be explained by the elevated rates of death and severe health problems in newborns born to unvaccinated mothers. The sickest babies had either died or had not left the hospital by the age of 4 weeks and therefore could not be readmitted, so these babies were excluded from the hospital readmission analysis.

McCullough’s post also fails to highlight the study’s other findings, which indicate no association between the vaccines and negative effects on newborns.

“The study finds that outcomes at birth are actually better for babies born following vaccination in pregnancy, and this finding is unchanged when the authors do additional analyses to take account of the fact that vaccinated families tend to have better healthcare in general,” Male said. The improvements for newborns included lower risk of severe problems such as hemorrhage or seizures, neonatal intensive care unit stays, and death.

It’s unclear how great of a role vaccines played in causing these lower risks. Maternal vaccination may have helped improve newborn outcomes by mitigating the risks associated with getting COVID-19 during pregnancy. But the authors of the paper wrote this was unlikely to fully explain the risk reductions they saw.

DeSilva and Vazquez-Benitez said that “healthy vaccinee bias,” in which people who get vaccines tend to be healthier and more likely to engage in healthy behaviors, could help explain the reduced risks of poor newborn health outcomes — despite attempts to adjust for these factors. They also pointed out that people who give birth earlier in their pregnancies will have less opportunity to get vaccinated. Being born too early can lead to health problems for babies.

Regardless, the reduced risk means it’s unlikely vaccination increased the risk of NICU stays, severe health problems or deaths in newborns, the researchers concluded. “It is at least reassuring that they are not elevated,” Jorgensen said.

McCullough had other critiques of the data used in the study. But he “misunderstands how the MOMBABY database works,” Male said. McCullough incorrectly wrote in his Substack post that if a mother delivered at one hospital and later took her baby to another hospital or clinic “for seizures, hemorrhage, etc.,” the pair wouldn’t be linked.

The MOMBABY database captures all hospitalizations in Ontario, Jorgensen said, so admission to any hospital in the province would be recorded and linked to the mother. The study was not meant to capture visits to clinics, which likely would be routine or for more minor issues.

Finally, McCullough pointed out that the study did not report on miscarriage or stillbirth. “That’s true: this study was not designed to look into that,” Male said. But other studies have shown no effect of COVID-19 vaccination on the rate of miscarriage. And as we’ve said, vaccination may reduce the risk of stillbirth.

COVID-19 Vaccination Benefits Mothers and Babies

McCullough also highlighted data showing similar rates of positive COVID-19 PCR test results during pregnancy among vaccinated and unvaccinated women, seemingly to back up his statement that the vaccines have no benefit during pregnancy.

However, the work “wasn’t designed as a study to look at vaccine effectiveness for pregnant women,” Jorgensen said. The data on COVID-19 testing were provided in a table describing characteristics of vaccinated versus unvaccinated pregnant women, which were used to adjust for differences between the groups.

Jorgensen, Male, DeSilva and Vazquez-Benitez all pointed out that in this study, there wasn’t information on whether the vaccinated women who tested positive for COVID-19 got vaccinated before or after getting sick. “We therefore can’t use this data to tell us anything about the effectiveness of COVID vaccination at preventing infection,” Male said.

Studies designed to look at COVID-19 vaccine effectiveness have found that it is similar whether the vaccines are given to pregnant or non-pregnant individuals. In the omicron era, vaccination has provided significant protection against severe disease and more limited protection against symptomatic illness — with booster doses improving effectiveness.

Furthermore, people who get vaccinated during pregnancy can pass on antibodies to their babies via the umbilical cord and subsequently via breast milk, although the level of protection provided by the breast milk antibodies is unclear. Maternal vaccination during pregnancy is associated with reduced risk of infection and hospitalization from COVID-19 during the first six months of a baby’s life, and particularly during the newborn period, according to multiple studies.

For instance, Jorgensen and her colleagues did a different study using the MOMBABY registry on the effects of maternal COVID-19 vaccination on babies during the first six months of life. Babies whose mothers had gotten the original primary vaccine series, including at least one dose during pregnancy, had a 45% lower risk of infection and 53% lower risk of hospitalization with omicron than babies of unvaccinated mothers. Protection was better if the mothers got at least one dose during the third trimester. With a booster dose during pregnancy, protection also increased, with babies having a 73% lower risk of infection and an 80% lower risk of hospitalization with omicron.

“Regardless of pregnancy status, COVID-19 vaccination remains the best protection against COVID-19-related hospitalization and death,” DeSilva and Vazquez-Benitez said. “In addition to reducing the risks of severe illness from COVID-19 in pregnant persons, COVID-19 vaccines administered during pregnancy can provide infants with antibodies against COVID before they are eligible to receive COVID-19 vaccines.”

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