Pfizer and its partner BioNTech have launched clinical trials to study the safety and effectiveness of its coronavirus vaccine on pregnant women.

In a news release, Pfizer said “the first participants have been dosed” in trials that aim to enrol 4,000 women worldwide. Besides studying whether the vaccine protects pregnant women, researchers will study the safety in infants of vaccinated women and whether protective antibodies were transferred to the infants. Infants will be monitored until they’re about 6 months old, the news release said. After a baby is born, the study will be unblinded and women who received placebo will be able to receive the vaccine. The study should conclude in January 2023.

“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,” said William Gruber MD, Pfizer’s senior vice president of vaccine clinical research and development. “We are deeply thankful to the volunteers who are enrolling in the trial, and site investigators who are leading this work.”

The study is important because of the lack of definitive guidance for pregnant women considering getting the vaccine. Pregnant women were not included in earlier clinical trials that resulted in the Pfizer vaccine receiving emergency use authorization from the FDA in December. COVID can be dangerous for expectant mothers. In November, the CDC said that pregnant women who contract the coronavirus are more likely to develop a severe form of the disease, die from COVID-19 and deliver prematurely.

Anthony Fauci, MD, recently said research shows pregnant women can safely receive the coronavirus vaccine. He said about 100,000 pregnant women in the United States have been vaccinated and none has shown serious side effects or exhibited any “red flags.” In December, the American College of Obstetricians and Gynecologists recommended the vaccines "should not be withheld from pregnant individuals” or “lactating individuals.” Moderna, which manufactures the only other coronavirus vaccine authorized for the U.S., created a registry to track pregnant women receiving the shot.

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