Describing the interim results from the Phase 2 test with 722 volunteers in the US and Honduras, the French-British partnership said its vaccine candidate achieved strong rates of neutralizing antibody responses, in line with those measured in people who have recovered from Covid. Higher levels were observed in the age group 18 to 59.

Volunteers for the trial that began in February 2021 included equivalent contingents aged 18 to 59 and 60 years and older, including people with high-risk medical conditions. Two injections were given 21 days apart, with three antigen dose levels of 5, 10 and 15 µg.  The fact that high neutralizing antibody levels were generated in participants with evidence of prior infection after a single injection suggests that the vaccine may have strong potential for development as a booster, the companies said.

The upcoming Phase 3 trial, which will be conducted with the 10 µg dose, will assess the efficacy of two vaccine formulations including the D614 (Wuhan) and B.1.351 (South African) variants. In parallel, the drugmakers plan to launch booster studies with various variant formulations to see whether a lower dose of the vaccine will generate a strong booster response regardless of the initial vaccine platform received.

Pending positive outcomes from the third study and regulatory reviews, Sanofi and GSK – the latter is providing the adjuvant for Sanofi’s formulation – said they expect their candidate to be approved as early as this year’s fourth quarter. Initially, they had hoped to have a shot finished by the third quarter, but late last year were compelled to restart the Phase 2 trial as Phase 2b when the vaccine showed a low immune response in older adults as a result of a weak antigen formulation.

Financial backing from BARDA for the French-British effort

The US Biomedical Advanced Research and Development Authority, (BARDA), the emergency preparedness arm of the Department of Health and Human Services, and the Defense Department are financially backing the joint effort of the two European players. In February 2020, BARDA awarded $2.1 billion to Sanofi to test a recombinant protein-based technology its Flublok influenza vaccine uses as a possible base for a Covid-19 vaccine – the flu shot also uses GSK's AS03 adjuvant. The BARDA funding was on top of the $256 billion the French company was already receiving for US vaccine development and reportedly was the highest awarded to any company under the Operation Warp Speed vaccine acceleration program.

Sanofi said its recombinant technology combined with GSK’s adjuvant is designed to offer the advantages of stability at temperatures used for routine vaccines, making it easily implementable and easier to distribute globally as it can be stored at normal refrigerator temperature. The French vaccine is also touted as offering the potential to generate high and sustained immune responses as well as the potential to prevent virus transmission.

In tandem with its Pasteur unit, Sanofi is the only company engaged threefold in Covid vaccine development. In a separate project, the Paris-based company is developing an mRNA candidate in partnership with US biotech Translate Bio. In March 2021, the two initiated a Phase 1/2 clinical trial to assess safety, immune response and reactogenicity after preclinical data showed high neutralizing antibody levels. First results are expected in this year’s third quarter.

Sanofi has also agreed to provide fill & finish support to three other Covid-19 vaccine producers. Starting this September it will manufacture up to 200 million doses of Moderna’s mRNa vaccine for the biotech’s US supply. The company has also signed on to make 125 million doses for BioNTech to pad the EU’s stockpile and has pledged to support Johnson & Johnson with some 12 million doses per month. For its own vaccines, it has purchasing agreements with the US, Canada, the EU and the UK and is also donating doses to the World Health Organization’s COVAX initiative.

Author: Dede Williams, Freelance Journalist