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COVID-19 vaccines appeared safe in pregnant women, with side effects that were consistent with those in non-pregnant people, researchers found.

In addition, though they were not directly comparable, incidence of reported adverse maternal and neonatal outcomes were similar to those reported prior to the pandemic, noted Tom Shimabukuro, MD, and colleagues from the CDC v-safe COVID-19 Pregnancy Registry Team in the .

Pregnant women were excluded from COVID-19 vaccine clinical trials, despite being at risk for adverse pregnancy outcomes and the CDC classifying pregnancy as a condition putting people at high risk for severe COVID-19. However, both CDC's Advisory Committee on Immunization Practices (ACIP) and the American College of Obstetricians and Gynecologists (ACOG) recommended that pregnant women should not be prevented from receiving COVID-19 vaccines, and advised shared clinical decision-making.

Establishing safety profiles for COVID-19 vaccines will help inform recommendations on maternal vaccination against COVID-19 going forward, the authors said.

The team examined data from three COVID-19 vaccine safety surveillance systems: CDC's v-safe smartphone-based post-vaccination symptom checker, the v-safe pregnancy registry, and the Vaccine Adverse Event Reporting System (VAERS).

Patients were eligible if they were 18 years or older, received one or two doses of Pfizer or Moderna's mRNA COVID-19 vaccine while pregnant or during periconception (defined as 30 days before to 14 days after), and did not identify their sex as male. Eligibility to be enrolled in v-safe's pregnancy registry was reviewed via telephone interview.

Overall, researchers examined data from 35,691 participants from Dec. 14, 2020 to Feb. 28, 2021. About 61-62% of participants were ages 25-34, and about three-quarters were non-Hispanic white. A large majority (86-87%) said they were pregnant at the time of vaccination.

Similar to non-pregnant people, injection-site pain, fatigue, headache, and myalgia were the most common adverse reactions, and were more common after the second dose. Only 1% of participants reported a fever (a temperature over 38º C) after the first dose, and 8% reported a fever after the second.

Pregnant women reported more nausea and vomiting after the second dose than non-pregnant women, but reactogenicity profiles were similar.

The v-safe pregnancy registry was comprised of 3,958 participants, mostly ages 25-34 and non-Hispanic white. Nearly all did not report a COVID-19 diagnosis during pregnancy. About 43% of participants were in their second trimester, with 29% in their first and 26% in their third.

There were 827 participants with a completed pregnancy, 86% of whom had a live birth. About 13% had a spontaneous abortion and around 1% had other outcomes, including induced abortion and ectopic pregnancy. Most spontaneous abortions occurred before 13 weeks.

Outcomes among 724 live-born infants, including 12 sets of multiple gestation, included preterm birth (9.4%), small for gestational age (3.2%), and major congenital anomalies (2.2%). There were no neonatal deaths reported. Among the 16 infants with congenital anomalies, no mothers received COVID-19 vaccine in the first trimester or periconception period.

There were 221 reports involving vaccinated pregnant women processed in VAERS, 70% of which involved non-pregnancy-specific adverse events. The most frequent pregnancy-related adverse event reported was spontaneous abortion (46 cases, 37 from first trimester), as well as stillbirth, premature rupture of membranes, and vaginal bleeding (three reports each). There were no congenital anomalies reported.

Shimabukuro's group noted that many of the participants in v-safe were included in phase 1a of vaccination distribution, including healthcare personnel. They noted that since v-safe is optional, it limits the generalizability of the data compared with previously published estimates, including likely differences in age, ethnic group, and clinical status.

"However, such comparisons are helpful to provide a crude sense of whether there are any unexpected safety signals in these early data," the authors wrote. The findings from these registries "do not indicate any obvious safety signals with respect to pregnancy or neonatal outcomes associated with COVID-19 vaccination in the third trimester."

Additionally, v-safe data were self-reported and may have been missing, which is a limitation. The authors could not evaluate adverse outcomes occurring in association with earlier pregnancy exposures, such as congenital anomalies, because no women vaccinated early in pregnancy has given birth in the v-safe pregnancy registry to date.

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