A global phase 2/3 study evaluating the Pfizer-BioNTech coronavirus disease 2019 (COVID-19) vaccine, BNT162b2, in preventing COVID-19 in healthy pregnant women has been initiated.

The randomized, placebo-controlled, observer-blind study (ClinicalTrials.gov: NCT04754594) is evaluating the safety, tolerability, and immunogenicity of BNT162b2 in approximately 4000 healthy pregnant women 18 years of age and older who are 24 to 34 weeks’ gestation. Participants will be randomly assigned 1:1 to receive 2 doses of BNT162b2 or placebo administered 21 days apart. Each woman will participate in the study for approximately 7 to 10 months, depending on whether they receive the vaccine or placebo.

The safety in infants of vaccinated pregnant women will be assessed, as well as the transfer of potentially protective antibodies to the infants. Infants will be monitored through approximately 6 months of age. After the birth of their child, maternal participants who received placebo will be unblinded and will receive the vaccine.

“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, Senior Vice President of Vaccine Clinical Research and Development, Pfizer. Prior to initiating this study, the Companies completed a developmental and reproductive toxicity study, which showed no evidence of fertility or reproductive toxicity in animals.

In December 2020, the Food and Drug Administration (FDA) granted Emergency Use Authorization (EUA) to Pfizer and BioNTech’s COVID-19 vaccine for active immunization against COVID-19 in individuals 16 years of age and older.

Additional studies of the vaccine in children 5 to 11 years of age and those younger than 5 years are expected to begin this year. Safety and efficacy data from a global phase 3 study (ClinicalTrials.gov: NCT04368728) in children 12 to 15 years of age is currently being evaluated; data is expected to be submitted to regulatory authorities in the second quarter of 2021.

In addition, Pfizer and BioNTech announced the submission of new data to the FDA demonstrating the stability of the vaccine when stored at -25°C to -15°C (-13°F to 5°F), temperatures more commonly found in pharmaceutical freezers and refrigerators. If the EUA label update is approved, it would allow for vaccine vials to be stored at these temperatures for a total of 2 weeks. Currently, the labeling states that the vaccine must be stored in an ultra-cold freezer at temperatures between -80ºC and -60ºC (-112ºF to ‑76ºF).


  1. Pfizer and BioNTech commence global clinical trial to evaluate COVID-19 vaccine in pregnant women. [press release]. New York, NY and Mainz, Germany: Pfizer, Inc. and BioNTech SE; February 18, 2021. 
  2. Pfizer and BioNTech submit COVID-19 vaccine stability data at standard freezer temperature to the US FDA. [press release]. New York, NY and Mainz, Germany: Pfizer, Inc and BioNTech SE; February 19, 2021.