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Clinical Context

Changes in cardiopulmonary and immunological physiology during pregnancy increase risk for COVID-19-related hospital/intensive care unit (ICU) admission, mechanical ventilation, and death. Severe COVID-19 increases adverse pregnancy outcomes, including hypertension, preeclampsia, impaired fetal growth, and preterm birth.

CANVAS was established during the 2009 influenza pandemic to provide rapid, real-time safety data during rollout of immunization programs. It has monitored COVID-19 vaccine safety since December 2020, when these vaccines first became available in Canada.

Study Synopsis and Perspective

Pregnant women should feel confident that the BNT162b2 and mRNA-1273 vaccines against COVID-19 are safe, according to a large new study published August 11.

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

This study, conducted by the Canadian National Vaccine Safety Network, looked at data from patients in 7 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. Individuals 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 to 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, British Columbia, Canada, led the study, which is one of the first to compare vaccine adverse effects (AEs) among 3 groups: vaccinated pregnant women, unvaccinated pregnant women, and vaccinated nonpregnant women.

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

The researchers found that 4% of pregnant women who received an mRNA vaccine reported a significant health event within a week after dose 1 and 7.3% after dose 2. The most common significant health events after dose 2 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 1 and 11.3% after dose 2. Serious health events were rare in all groups (< 1%) and occurred at similar rates in all 3 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 Centers for Disease Control and Prevention (CDC), who were not involved in the study, wrote in a linked editorial that the findings are consistent with a growing body of evidence that COVID-19 mRNA vaccines are safe in pregnancy.

Diana Gillman, MD, with the obstetrics and gynecology department of Olmstead Medical Center in Rochester, Minnesota, said 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 said.

"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 added.

Gillman said 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."

Lancet Infect Dis. Published online August 11, 2022.^[1]

Clinical Implications

• COVID-19 mRNA vaccines have a good safety profile in pregnancy, with significant health events lower in pregnant people than in age-matched nonpregnant vaccine recipients.
• These data can appropriately inform pregnant women regarding reactogenicity of COVID-19 vaccines during pregnancy.
• Implications for the Healthcare Team: Given the increased rate of significant complications of COVID-19 in pregnancy, the healthcare team should educate patients that high vaccine coverage is important to protect the mother and newborn.

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