Pfizer and BioNTech have reported positive early data from a Phase II/III clinical trial of their Omicron BA.4/BA.5-adapted bivalent Covid-19 vaccine (Pfizer-BioNTech COVID-19 Vaccine, Bivalent (Original and Omicron BA.4/BA.5)) in people aged 18 years and above.

The randomised, multi-centre, controlled trial has enrolled approximately 900 healthy volunteers.

Subjects aged 18 and above were given either a 30-µg or 60-µg booster dose of the companies’ Omicron BA.4/BA.5-adapted Covid-19 vaccine.

A 30-µg booster dose of the same vaccine was administered to participants aged 12 to 17 years.

Pfizer and BioNTech will make comparisons with a control group to support potential full licensure and registrations of the vaccine across the globe. This control group also received a fourth dose with the original vaccine.

A substantial rise in the Omicron BA.4/BA.5 neutralising antibody response was observed above pre-booster levels with a 30-µg booster dose of the bivalent vaccine.

This observation was based on sera obtained seven days after administration and similar responses were reported across individuals aged 18 to 55 years, and those who are above 55 years.

Based on this, Pfizer and BioNTech reported that a 30-µg booster dose of the Omicron BA.4/BA.5-adapted bivalent vaccine is expected to provide better protection against the Omicron BA.4 and BA.5 variants.

Pfizer chairman and CEO Albert Bourla said: “While we expect more mature immune response data from the clinical trial of our Omicron BA.4/BA.5-adapted bivalent vaccine in the coming weeks, we are pleased to see encouraging responses just one week after vaccination in younger and older adults.

“These early data suggest that our bivalent vaccine is anticipated to provide better protection against currently circulating variants than the original vaccine, and potentially help to curb future surges in cases this winter.”

The companies expect additional data measuring responses at one month after the booster dose administration in the coming weeks.

In June this year, Pfizer and BioNTech reported that two Omicron-adapted Covid-19 vaccine candidates demonstrated a greater immune response against Omicron BA.1 compared with their existing vaccine in a Phase II/III trial.