Pfizer and BioNTech have commenced a global Phase 2/3 study to further evaluate their Covid-19 vaccine candidate, BNT162b2, in healthy pregnant women.

The randomised, placebo-controlled, observer-blind Phase 2/3 study is designed to enrol nearly 4,000 healthy pregnant women, aged 18 years and older, and vaccinate them during 24 to 34 weeks of gestation.

The study will evaluate the safety, tolerability, and immunogenicity of two doses of BNT162b2, administered 21 days apart, compared to placebo.

Also, the study will assess the safety in infants of vaccinated pregnant women and monitor the transfer of potentially protective antibody to their infants.

Pfizer vaccine clinical research and development senior vice president William Gruber said: “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.

“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.”

Prior to the Covid-19 vaccine clinical trial in pregnant women, Pfizer and BioNTech have conducted developmental and reproductive toxicity (DART) study with BNT162b2.

The DART study, which was required by the regulatory authorities to begin the study in pregnant women, has shown no evidence of fertility or reproductive toxicity in animals.

Pfizer is leveraging its expertise in conducting clinical trials in pregnant women, supported by its experience from its ongoing Phase 3 Respiratory Syncytial Virus vaccine, and Phase 2 Invasive Group B Streptococcus Infection trials.

Furthermore, Pfizer and BioNTech intend to conduct additional studies in children, aged between five and 11 years, in the coming few months, and in children younger than five years, later in 2021.

The Pfizer-BioNTech Covid-19 vaccine has not been approved or licensed by the US Food and Drug Administration (FDA) but has been granted an Emergency Use Authorisation (EUA) by FDA, to prevent Covid-19 in people aged 16 years and older.

BioNTech chief medical officer Özlem Türeci said: “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.”