Sanofi, GSK post 58% efficacy in omicron-affected COVID-19 vaccine trial, teeing up race to regulators

Sanofi and GlaxoSmithKline are nearly ready to seek approval for their COVID-19 vaccine. After suffering a delay late in 2020, the partners have linked two doses of the protein vaccine to 58% protection from symptomatic COVID-19 in a variant-affected phase 3 clinical trial.

The efficacy figure is well down on the 90%-plus protection rates achieved by the Pfizer-BioNTech and  Moderna vaccines, but that cross-trial comparison has little value given the changes in the SARS-CoV-2 virus between the studies. The mRNA vaccine trials took place before the spread of variants of concern. The Sanofi-GSK trial covered a period in which the delta and omicron variants were prevalent.

“No other global phase 3 efficacy study has been undertaken during this period with so many variants of concern, including omicron, and these efficacy data are similar to the recent clinical data from authorized vaccines,” Thomas Triomphe, executive vice president at Sanofi Vaccines, said in a statement.

Sanofi and GSK are yet to provide a full breakdown of how the vaccine held up against different variants, but there are signs omicron, a variant known to partly evade approved vaccines, dragged down efficacy. Early sequencing data indicate the vaccine provided 77% protection against symptomatic delta infection.

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With two doses achieving 100% efficacy against severe COVID-19 and hospitalization and 75% efficacy against moderate to severe disease, Sanofi and GSK plan to use the data as the basis for approval filings. Talks with U.S. and European regulatory agencies are underway.

The opportunity for the vaccine as a primary series in Europe and the U.S. is limited, with most people already receiving one of the existing products. But there may be more opportunities for the refrigerator temperature-stable adjuvanted recombinant protein-based vaccine in parts of the world in which the cold chain requirements of the mRNA vaccines are a barrier to access.

Sanofi and GSK also plan to send regulators data on the use of their vaccine as a booster. The study evaluated the effect of giving a Sanofi-GSK booster vaccine to people who received a range of products as their primary series. In adults aged 18 to 55 years, the booster increased neutralizing antibodies by between nine times in recipients of Moderna’s vaccine to 84 times in recipients of the Sanofi-GSK vaccine. The range of antibody increases in older adults spanned from 11 to 153 times.