The phase 2/3 study will test approximately 4,000 healthy, pregnant women 18 years of age or older, according to Pfizer and BioNTech. The women will get the shot between 24 to 34 weeks of gestation in the randomized, placebo-controlled, observer-blind trial.
Pfizer’s mRNA vaccine requires two doses spaced apart approximately 21 days. Some of the women will get the two doses; others will get a placebo administered three weeks apart. Volunteers will be drawn from multiple countries, including the United States, Argentina, and South Africa.
“We are proud to start this study in pregnant women and continue to gather the evidence on safety and efficacy to potentially support the use of the vaccine by important subpopulations,” Dr. William Gruber senior vice president of Vaccine Clinical Research and Development at Pfizer, said in a statement. “Pregnant women have an increased risk of complications and developing severe COVID-19, which is why it is critical that we develop a vaccine that is safe and effective for this population. We are deeply thankful to the volunteers who are enrolling in the trial, and site investigators who are leading this work.”
“Enabling broad access to our highly effective COVID-19 vaccine is an important goal for us. Now that we are seeing successful initial implementation of vaccine campaigns with BNT162b2 across the globe, it is time to take the next step and extend our clinical program to other vulnerable populations, such as pregnant women, to potentially protect both them and future generations,” added Dr. Özlem Türeci, chief medical officer for BioNTech.
The women will participate in the study for 7 to 10 months, as researchers evaluate safety in the infants of the vaccinated women and whether protective antibodies are transferred to the babies. The infants will be monitored until they’re about 6 months old.
After a woman’s baby is born, she will get a vaccine if she previously received a placebo.
Pfizer’s shot is one of two to receive emergency authorization in the U.S. by drug regulators.
The Food and Drug Administration required Pfizer to conduct at least one post-authorization study to evaluate the association between its vaccine and a list of adverse events, along with deaths and hospitalizations. The study population was also recommended to include pregnant women.
Available data for the vaccine administered to pregnant women “are insufficient to inform vaccine-associated risks in pregnancy,” the FDA said in a fact sheet about the authorization. In a memo about the vaccine, officials added: “There are currently insufficient data to make conclusions about the safety of the vaccine in subpopulations such as children less than 16 years of age, pregnant and lactating individuals, and immunocompromised individuals.”
If women are pregnant or plan to become pregnant, they should tell their vaccination provider before getting a COVID-19 vaccine.