The Centers for Disease Control and Prevention (CDC) is recommending that pregnant women receive a COVID-19 vaccination.
"CDC recommends that pregnant people receive the COVID-19 vaccine. We know that this is a deeply personal decision, and I encourage people to talk to their doctors or primary care providers to determine what is best for them and for their baby," Dr. Rochelle Walensky, the health agency's head, said in a virtual briefing on April 23.
The recommendation is an update from previous guidance, which advised pregnant women that they may choose to be vaccinated, but did not recommend doing so.
Two of the three vaccines authorized for emergency use in the United States—one from Moderna and one from Pfizer-BioNTech—are built on messenger RNA (mRNA) technology.
Researchers examined data from the v-safe pregnancy registry and the passive Vaccine Adverse Event Reporting System (VAERS). They took into account survey data for 30,887 people who identified as pregnant in the registry and got one of the mRNA vaccines, as well as nearly 5,000 others who found they were pregnant after getting a vaccine.
A subset numbering 3,958 of the registry users answered questions from the v-safe registry call center. Of those users, nearly 98 percent reported not having a COVID-19 infection.
Another 56 reported having COVID-19 before vaccination, while 22 contracted the illness after vaccination, including 12 who contracted it two or more weeks after receiving the vaccine.
Among 827 women who had completed pregnancy, 712 gave live birth, while the bulk of the remaining cases saw the pregnancy end in a "spontaneous abortion," a term the study used to describe miscarriages taking place within 20 weeks of gestation. Adverse outcomes among the infants who were born included 60 cases of preterm birth, 23 cases of small size for gestational age, and 16 cases of major congenital anomalies. No neonatal deaths among the live births were reported. One case of stillbirth was recorded.
Dozens of cases of post-vaccination miscarriages have been reported to VAERS. That's the most common pregnancy-specific condition reported to the system after vaccination.
Proportions of pregnancy and neonatal outcomes in pregnant women who got vaccinated and had a live birth appeared similar to incidences published in the peer-reviewed literature previous to the pandemic, the CDC researchers said.
"Pregnant people experienced the same side effects as others following vaccination. We were also able to follow, in detail, more than 3,900 pregnant women, and over 800 of whom have completed their pregnancies. Importantly, no safety concerns were observed for people vaccinated in the third trimester or safety concerns for their babies," Walensky said during the briefing.
Limitations of the study included a reluctance by many who identified as pregnant to answer questions, the passive nature of the vaccine reporting system, and a lack of knowledge about the total number of COVID-19 vaccine doses administered to pregnant women.
However, early data indicated that COVID-19 vaccines not only protect women against the disease and its complications during pregnancy, but also pass on antibodies to their children as well, if they receive the vaccine in their third trimester, the researchers said.
"Emerging evidence has shown transplacental transfer of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies after maternal Covid-19 vaccination during the third trimester, which suggests that maternal vaccination might provide some level of protection to the neonate," the researchers wrote.
"Continued monitoring is needed to further assess maternal, pregnancy, neonatal, and childhood outcomes associated with maternal COVID-19 vaccination, including in earlier stages of pregnancy and during the preconception period. Meanwhile, the present data can help inform decision making about vaccination by pregnant persons and their health care providers."
When compared to non-pregnant people, pregnant women are at increased risk for severe illness from COVID-19, according to the CDC. However, the overall risk of severe illness is low.