Preliminary results from the VAT0002 clinical trial for the vaccine as a booster shot showed neutralizing antibodies increased 9- to 43-fold, regardless of the primary vaccine received or the age of the individual (the vaccine was tested as a booster after AstraZeneca, J&J, Pfizer and Moderna vaccines).
The booster was well tolerated, with a safety profile similar to currently approved COVID-19 vaccines.
Booster being tested against Omicron
Sanofi and GSK partnered up early in the pandemic to develop the recombinant protein-based vaccine, using Sanofi's recombinant antigen and GSK's pandemic adjuvant. The project, however, suffered a setback at the end of last year with the initial candidate failing to generate a sufficient immune response in older people.
A refined antigen formulation entered Phase 2 trials in February, with interim results showing high rates of neutralizing antibody responses in all adult age groups.
Sanofi and GSK are now assessing two formulations in Phase 3 trials: one against the original D614 parent virus and a second bivalent formulation which also adds the spike protein of the B.1.351 (Beta) variant. The VAT0002 booster trial used a 5µg dose of the first monovalent formulation, administered between four and ten months after a complete primary vaccination schedule.
Additional trial cohorts are assessing the bivalent formulation with data expected during the first half of 2022.
The Omicron variant was not circulating during the booster trial: but the companies are using sera from trial participants to establish the ability of the vaccine to cross-neutralize against Omicron.
Phase 3 trial update
Meanwhile, the companies’ ongoing Phase 3 trial, VAT0008, is expected to continue into 2022 with results in Q1. Regulatory authorities require efficacy to be demonstrated in naïve seronegative populations, with the trial taking place across the US, Asia, Africa and Latin America. The trial recruited most of its participants in Q3, 2021: coinciding with a significant increase in COVID-19 infections globally due to the Delta variant.
During its last review, the independent Data Safety Monitoring Board identified no safety concerns and recommended the trial to continue into early 2022 to accrue more data.
This pushes potential regulatory approval for the vaccine into 2022, back from the companies’ initial hopes of Q4 2021 approval when they launched the Phase 3 trial in May.