Novavax has reported topline results from its Phase III clinical trial assessing Omicron subvariant vaccine candidates for Covid-19.

In the two-part, observer-blinded, randomised Phase III Omicron trial, NVX-CoV2515 (BA.1) and bivalent (NVX-CoV2373 + Omicron subvariant NVX-CoV2515) vaccines were compared to NVX-CoV2373 in adult subjects aged 18 to 64.

All formulations include the company’s saponin-based Matrix-M adjuvant for improving and broadening the immune response.

Designed to evaluate the reactogenicity and immune responses to all three formulations, the trial plans to enrol 2,090 adults across 19 Australian sites.

The primary endpoints of the trial include measures of immune response while additional immune response measurements and safety measures are the secondary endpoints.

The boosting trial for the SARS-CoV-2 rS variant vaccines demonstrated that Novavax’s NVX-CoV2515 met the primary strain-change endpoint.

It was also observed that this BA.1 vaccine candidate’s neutralising responses in subjects who were not exposed to Covid-19 earlier were greater than those of NVX-CoV2373.

The trial data also showed no benefit for the Novavax bivalent vaccine candidate against the BA.1 vaccine candidate or prototype vaccine in the overall subjects.

Across the three vaccine groups, immunoglobulin G (IgG) antibody responses against BA.1 and prototype strains showed similar responses.

The results demonstrated that the prototype vaccine induced a broad immune response against the original prototype, BA.1, and BA.5 strains, and strong IgG responses to both BA.1 and the matched prototype strain.

Novavax Research and Development president Gregory Glenn said: “Today’s results show that use of our prototype vaccine as a booster induces cross-reactive responses to a broad range of variants with the potential to protect against future strains.

“Our vaccine, which provides a broad immune response, even in the face of evolving variants, presents a potential strategy to protect against Covid-19 now and into the future.”

All three vaccine formulations were found to be consistent with the safety profile of the prototype vaccine, similarly well-tolerated, when given as a fourth dose.

In August this year, Novavax started the Phase IIb/III Hummingbird clinical trial of NVX-CoV2373 in younger children aged six months to 11 years.