mRNA Covid-19 Vaccines in Pregnant Women

Abstract

T h e ne w e ngl a nd jou r na l o f m e dicine n engl j med 384;24 nejm.org After Emergency Use Authorization was granted for the messenger RNA (mRNA) vaccines BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna), persons at the highest risk for coro-navirus disease 2019 (Covid-19)-related illness and death were prioritized for vaccination. 1 Among these were pregnant women, yet they had been excluded from initial vaccine trials. Pregnant women and their clinicians were left to weigh the documented risks of Covid-19 infection against the unknown safety risks of vaccination in deciding whether to receive the vaccine. Before the vaccine rollout, multiple cohort studies documented that pregnant women were at greater risk than nonpregnant women for severe disease after Covid-19 infection, resulting in intensive care unit admission, mechanical ventilation , and death. 2,3 Pregnant women with co-existing illnesses such as diabetes, hyperten-sion, and obesity were recognized to be at even greater risk. 4 Studies also showed an increased risk of pregnancy complications-including preterm birth, cesarean delivery, and preeclamp-sia-associated with Covid-19 infection during pregnancy. 5 Therefore, clinicians relied on developmental and reproductive animal data from Moderna that showed no safety concerns, and there was no biologically plausible reason that the mRNA technology would be harmful in pregnancy. Pregnant women were counseled to consider the available evidence and make personal decisions about vaccination in the absence of human safety data. In this issue of the Journal, Shimabukuro et al. 6 provide much-needed preliminary data on the safety of these vaccines in pregnancy on the basis of the v-safe surveillance system and pregnancy registry. V-safe, a new smartphone-based surveillance system from the Centers for Disease Control and Prevention that is available to all Covid-19 vaccine recipients, sends text messages to assess general health and pregnancy status during a period of 12 months after vaccination. Persons who identify as pregnant can enroll in the v-safe pregnancy registry, which contacts participants by telephone to answer in-depth questions. The report by Shimabukuro et al. includes safety results for 35,691 v-safe participants 16 to 54 years of age who identified as pregnant and the first 3958 participants who enrolled in the v-safe pregnancy registry. In both cohorts, 54% of the participants received the Pfizer-BioNTech vaccine and 46% received the Moderna vaccine. The age distribution, status with respect to race and ethnic group, and timing of the first dose were similar with each vaccine. Among v-safe participants, 86.5% had a known pregnancy at the time of vaccination, and 13.5% reported a positive pregnancy test after vaccination. Among v-safe pregnancy registry participants, 28.6% received vaccine in the first trimester, 43.3% in the second trimester, and 25.7% in the third trimester. Among 827 registry participants who reported a completed pregnancy, the pregnancy resulted in a spontaneous abortion in 104 (12.6%) and in stillbirth in 1 (0.1%); these percentages are well within the range expected as an outcome for this age group of persons whose other underlying medical conditions are unknown. A total of The New England Journal of Medicine Downloaded from nejm.org on June 22, 2021. For personal use only. No other uses without permission.