Pfizer to Study COVID-19 Vaccine in Pregnant Women

Pfizer and BioNTech recently announced that the first participants have been dosed in a global Phase 2/3 study to further evaluate their COVID-19 vaccine in healthy pregnant women.

The randomized, placebo-controlled study will uncover the safety, tolerability, and immunogenicity of two doses of the vaccine, BNT162b2, in 4,000 pregnant women 18 years of age and older. Researchers will vaccinate trial participants between 24 to 34 weeks of gestation.

Each woman will also participate in the study for nearly seven to ten months, depending on whether she receives BNT162b2 or a placebo. 

Additionally, the study will assess safety in infants of vaccinated pregnant women as well as the transfer of potentially protective antibodies to their infants, Pfizer explained. But once an infant is born, maternal trial participants will be unblinded and those who were in the placebo group will receive the vaccine. 

“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,” William Gruber MD, senior vice president of vaccine clinical research and development at Pfizer, said in the announcement.

“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,” Gruber continued.

Before conducting their vaccine trial in pregnant women, regulatory authorities required Pfizer and BioNTech to complete a developmental and reproductive toxicity (DART) study with BNT162b2. 

Notably, the study showed no sign of fertility or reproductive toxicity in animals.   

Pfizer is leveraging its expertise in conducting clinical trials for vaccine candidates against respiratory syncytial virus and invasive group B streptococcus infection to conduct the trials in pregnant women. 

At the end of June, Pfizer announced the initiation of four Phase 3 clinical trials for its various vaccine candidates, including one study for its respiratory syncytial virus vaccine candidate, RSVpreF.

The study enrolled 6,900 pregnant women aged 18 to 49 years to evaluate the safety and efficacy of RSVpreF in infants born to immunized pregnant women compared to placebo. Just two months before the launch of the trial, positive top-line results were achieved for a Phase 2b proof-of-concept study of RSVpreF. 

Pfizer and BioNTech expect to start additional studies of BNT162b2in children between the ages of five and 11 years over the next couple of months and in children younger than five later this year.

Currently, safety and efficacy of the vaccine in individuals 12 to 15 years of age are being evaluated in the global Phase 3 study (C4591001) and any relevant data will be submitted to the regulatory authorities in the second quarter of 2021, Pfizer said.

Additionally, the companies expect to launch studies to further evaluate the vaccine in people with compromised immune systems.

“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,” said Özlem Türeci, MD, chief medical officer of BioNTech.

At the beginning of May, Pfizer and BioNTech dosed the first participants in their BNT162 vaccine program to prevent COVID-19. 

Since then, one-dose of BNT162b2 was found to be 95 percent effective in participants without prior SARS-CoV-2 infection, as well as with and without prior SARS-CoV-2 infection in November. And a two-dose regimen elicited 95 percent protection against COVID-19 in individuals 16 years of age and older in December.