Daily Fact-Check: COVID-19 Vaccination During Pregnancy Is Safe, Has Multiple Benefits

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.