In an early analysis of coronavirus vaccine safety data, researchers from the Centers for Disease Control and Prevention found no evidence that the Pfizer-BioNTech or Moderna vaccines posed a serious risk during pregnancy.
The results are preliminary and only cover the first 11 weeks of the US vaccination program. The study, which included self-reported data on more than 35,000 people who received any of the vaccines during or shortly before pregnancy, is the largest to date on the safety of coronavirus vaccines in pregnant women.
Pregnant women were excluded during clinical trials with the vaccines. Patients, doctors and experts were therefore unsure whether the shots could be safely administered during pregnancy.
"There is great concern about whether it is safe and whether it would work and what to expect in the event of side effects," said Dr. Stephanie Gaw, Maternal-Fetal Medicine Specialist at the University of California at San Francisco.
The new data, said Dr. Gaw, show that "many pregnant people receive the vaccine, that the undesirable effects of pregnancy do not increase significantly at this point, and that the side effect profiles are not very similar to pregnant people."
"I think this is all very comforting," she said, "and I think it will really help public health providers and officials recommend the vaccine more strongly during pregnancy."
Covid-19 carries serious risks during pregnancy. Pregnant women who develop symptoms of the disease are more likely to get seriously ill and die than non-pregnant women with symptoms.
Because of these risks, the C.D.C. has recommended providing coronavirus vaccines to pregnant women, but also suggests that they consult their doctor when deciding whether to vaccinate.
The new study, published Wednesday in the New England Journal of Medicine, is largely based on self-reported data from V-safe, C.D.C.'s coronavirus vaccine safety monitoring system. Participants in the program use a smartphone app to regularly conduct surveys about their health and possible side effects after receiving a Covid-19 vaccine.
The researchers analyzed the side effects of V-Safe participants who received either the Pfizer or Moderna vaccine between December 14, 2020 and February 28, 2021. They focused on 35,691 participants who said they were pregnant when they received the vaccine or became pregnant shortly afterwards.
After vaccination, pregnant participants reported the same general pattern of side effects as non-pregnant women, the researchers noted: injection site pain, fatigue, headache, and muscle pain.
What You Need To Know About The Johnson & Johnson Vaccine Break In The United States
- On April 13, 2021, U.S. health officials called for an immediate halt to use of Johnson & Johnson's single-dose Covid-19 vaccine after six recipients in the U.S. developed a rare blood clot disorder within one to three weeks of being vaccinated.
- All 50 states, Washington, DC, and Puerto Rico have temporarily stopped using the vaccine or recommended providers are suspending use of the vaccine. The U.S. military, government-run vaccination centers, and a variety of private companies, including CVS, Walgreens, Rite Aid, Walmart, and Publix, also paused the injections.
- Fewer than one in a million Johnson & Johnson vaccinations are currently being studied. If there is a real risk of blood clots from the vaccine – which has yet to be determined – the risk is extremely small. The risk of contracting Covid-19 in the United States is much higher.
- The hiatus could complicate the country's vaccination efforts at a time when many states are facing spikes in new cases and are trying to address vaccine hesitation.
- Johnson & Johnson had also decided to delay the launch of its vaccine in Europe amid concerns about rare blood clots. However, the company later decided to continue its campaign after the European Union Medicines Agency announced the addition of a warning. South Africa, devastated by a contagious variant of the virus, stopped using the vaccine and Australia announced it would not buy doses.
Women who were pregnant were slightly more likely to report injection site pain than women who did not, but were less likely to report the other side effects. They were also slightly more likely to report nausea or vomiting after the second dose.
Pregnant V-safe participants also had the option of enrolling in a special register in which the results of pregnancy and infant were recorded.
By the end of February, 827 of the people entered in the pregnancy register had completed their pregnancy, of which 86 percent resulted in a live birth. The incidence of miscarriages, premature births, low birth weight, and birth defects were consistent with those reported in pregnant women before the pandemic, the researchers report.
"This study is critical for pregnant people," said Dr. Michal Elovitz, a maternal-fetal medicine specialist at the University of Pennsylvania, in an email. "It's very comforting that no acute events have been reported in pregnant people," she said as the study progressed.
However, the report has several caveats, and experts say a lot more research is needed. Participation in the monitoring programs is voluntary and the data is reported by yourself.
Since the study period only spanned the first few months of the US vaccination campaign, the vast majority of those on the pregnancy registry were healthcare workers. And there is still no data on pregnancy outcomes for people vaccinated in the first trimester of pregnancy.
"I think we can feel more secure if we recommend the vaccine during pregnancy, especially in pregnant people who are at risk of Covid," said Dr. Gaw. "But we do I will have to wait for more data to get full pregnancy results from early pregnancy vaccines. "