Novavax has started patient enrolment in a Phase III trial (Prepare) of its respiratory syncytial virus F-protein nanoparticle vaccine candidate (RSV F Vaccine) in pregnant women, to protect infants via maternal immunisation.

The company is focused on the discovery, development, and commercialisation of recombinant nanoparticle vaccines and adjuvants.

The Prepare trial uses a group sequential design, which offers flexibility in trial size depending on the rate of endpoint events and evolving evidence of efficacy, while maintaining the trial’s blinding integrity.

"We believe that maternal immunisation offers the optimal way of protecting young infants."

The company noted that the eventual sample size may vary between 5,000 and 8,255 pregnant women, over a period of two to four years.

The participants in the trial are being vaccinated at a number of global clinical sites in advance of each region’s RSV season.

To support the RSV F Vaccine Phase III trial in pregnant women, the company has also secured an $89m grant from the Bill & Melinda Gates Foundation.

The trial’s primary objective is to determine the efficacy of maternal immunisation with the RSV F Vaccine. It is being used to treat symptomatic RSV lower respiratory tract infection (LRTI) with hypoxemia in infants under 90 days old.

The US Food and Drug Administration (FDA) recently finalised the trial’s objectives, endpoints, and statistical approach.

Novavax president and CEO Stanley Erck said: "We believe that maternal immunisation offers the optimal way of protecting young infants, who are among the most susceptible populations to RSV disease.

"Initiation of this trial builds on our groundbreaking Phase II clinical data in this important population, and incorporates discussions with experts in the field and the FDA.

"The initiation of our second pivotal Phase III trial this quarter, ahead of our guidance, demonstrates the ability of our team to execute along aggressive timelines."

Results from the company’s Phase II trial in pregnant women provided the basis for the Phase III trial design, including the determination of anti-RSV antibody responses in mothers and antibody transfer from mothers to infants.