Aug. 11, 2022 – Pregnant women should feel confident that Pfizer’s and Moderna’s vaccines against COVID-19 are safe, according to a large new study published today.

In fact, pregnant vaccinated women had lower odds of a significant health event, compared with nonpregnant vaccinated women, after both doses of either mRNA vaccination, the researchers reported in the journalThe Lancet Infectious Diseases.

This study, done by the Canadian National Vaccine Safety Network, looked at data from patients in seven Canadian provinces and territories between December 2020 and November 2021.

All vaccinated people in the study were asked to report any health events during the week after each COVID-19 vaccine dose. Those in the unvaccinated pregnant control group were asked to record any health problems over the 7 days before they completed the survey.

In all, 191,360 women ages 15-49 years old completed the first dose survey and 94,937 completed the second dose survey.

Manish Sadarangani, from the British Columbia Children’s Hospital Research Institute in Vancouver, led the study, which is one of the first to compare vaccine side effects among three groups: vaccinated pregnant women, unvaccinated pregnant women, and vaccinated nonpregnant women.

Study authors note that the pandemic has disproportionately affected pregnant women, who are at higher risk of severe COVID-19 disease, compared with nonpregnant people in their age group.

Adverse Events Low Across Groups

The researchers found that 4% of pregnant women who got an mRNA vaccine reported a significant health event within a week after dose one and 7.3% after dose two. The most common significant health events after dose two were a general feeling of being unwell, headache/migraine, and respiratory infection.

For pregnant unvaccinated women, 3.2% reported similar events in the week before taking the survey.

In the control group of nonpregnant but vaccinated women, 6.3% reported a significant health event in the week after dose one and 11.3% after dose two. Serious health events were rare in all groups (fewer than 1%) and occurred at similar rates in all three groups.

There was no significant difference among miscarriage/stillbirth rates among the groups.

Investigators defined “significant health event” as a new or worse health event that was enough to cause the patient to miss school or work, require medical consultation, and/or prevent daily activities in the previous week. “Serious health event” was defined as resulting in an emergency department visit and/or hospitalization in the previous week.

Sascha Ellington, PhD, and Christine Olson, MD, from the CDC, who were not involved in the study, write in a linked editorial that the findings are consistent with a growing body of evidence that COVID-19 mRNA vaccines are safe in pregnancy.

Even With Good Science, Convincing is Tough

Diana Gillman, MD, with the Obstetrics and Gynecology Department of Olmstead Medical Center in Rochester, MN, says even these results may not convince all pregnant women to get vaccinated because of continued, unfounded fears surrounding the vaccines.

“Unfortunately, although this study confirms what we already know about COVID vaccine in pregnancy – it is safe and effective in preventing possible life-threatening illness in mother and baby – many patients in the U.S. continue to be resistant to being vaccinated during pregnancy as a result of unfounded fears of fetal harm,” she says.

“Patients routinely accept their medical provider’s advice on everything else in pregnancy, including, in this country, receiving the Tdap vaccine at 28 weeks, which works to protect the baby from whooping cough in infancy by evoking maternal antibodies that pass to the fetus in utero, yet they resist this potentially life-saving inoculation.”

Gillman says data on convincing parents that COVID-19 vaccines are safe will likely now need to come from experts in psychology and sociology who can pinpoint why patients resist and what strategies will work.

Scientifically,” she says, “we have it covered.”