COVID-19 boosters do not increase miscarriage risk

A case-control surveillance study has found no link between monovalent COVID-19 boosters and miscarriage before 20 weeks of pregnancy.

In this study which predates the availability of bivalent boosters, receipt of a monovalent COVID-19 booster shot in a 28-day, or 42-day exposure window did not increase the chances of miscarriage in over 100,000 women at 6–19 weeks of pregnancy.

“COVID infection during pregnancy increases the risk of poor outcomes, yet many people who are pregnant or thinking about getting pregnant are hesitant to get a booster dose because of questions about safety,” said Dr Elyse Kharbanda, senior investigator at HealthPartners Institute in Minnesota, US and lead author of the study.

“Our findings clearly support the safety of recommendations for COVID-19 booster vaccination in early pregnancy,” she said. “However, ongoing vaccine surveillance work is important because it provides reassurance and helps people feel confident in their vaccinations.”

4-6 weeks after booster vaccination

Kharbanda and her team examined data on 112, 718 unique pregnancies from eight health systems in the Vaccine Safety Datalink (VSD). Women were aged 16–49 years of age with pregnancies at 6–19 weeks’ gestation. Spontaneous abortion cases and ongoing pregnancy were evaluated at several surveillance periods from November 2021 to June 2022. [JAMA Network Open 2023;6(5):e2314350]

Generalized estimating equations were used to estimate adjusted odds ratios (aOR). Gestational age, maternal age, antenatal visits, race and ethnicity, site, and surveillance period were used as covariates and robust variance estimates to account for inclusion of multiple pregnancy periods for every unique pregnancy.

The study included pregnant women of Asian, non-Hispanic, Hispanic, White, and Black descent.   Women were followed up during a 28-day and a 42-day window periods. Among 270,853 pregnancy-period controls, 11, 095 had received a third mRNA COVID-19 vaccine in a 28-day window. Among 14,226 cases who had spontaneous abortion during the study period, 553 had received a third mRNA COVID-19 vaccine within 28 days of the abortion.

No link between vaccination and abortion

Receipt of a third mRNA COVID-19 vaccine was not associated with spontaneous abortion in a 28-day window (aOR, 0.94, 95 percent confidence interval [CI], 0.86-1.03).

Results were consistent with that for a 42-day window (aOR, 0.97, 95 percent CI, 0.90–1.05). The same was true for any COVID-19 booster in a 28-day (aOR, 0.94, 95 percent CI, 0.86–1.02) or 42-day (aOR, 0.96, 95 percent CI, 0.89–1.04) exposure window.

“The risk of miscarriage following a booster dose was similar to the risk seen after a first or second mRNA vaccine dose (aOR, 1.02; 95 percent CI, 0.96–1.08), which we had previously studied,” said Kharbanda.

With the US FDA approval of the bivalent COVID-19 booster vaccines on September 1, 2022, studies of bivalent booster vaccine exposures in early pregnancy are ongoing. “Results of these studies will be important,” she added.