The vaccine is based on Sanofi’s recombinant technology and GSK’s pandemic adjuvant. It is designed to trigger high and consistent immune responses, as well as potentially stop virus transmission.
In the global randomised, double-blind, placebo-controlled Phase III trial, the vaccine’s safety, efficacy and immunogenicity will be evaluated in a total of around 35,000 subjects aged 18 and above.
It will be performed at sites in the US, Asia, Africa and Latin America.
The two-stage design of the trial will first assess the efficacy of a vaccine formulation targeting the original Wuhan variant (D.614). The second stage will investigate a different formulation using the South African variant (B.1.351).
According to recent scientific data, antibodies generated against the South African variant may offer wider cross-protection against other variants that are more transmissible.
The trial design is intended to facilitate testing of the vaccine’s efficacy against different circulating variants.
Sanofi Pasteur executive vice-president and global head Thomas Triomphe said: “We are encouraged to see first vaccinations starting to take place in such an important, pivotal Phase III study, as we believe that our unique technology platform will provide a clinically-relevant vaccine option.
“We have adapted our vaccine development strategy based on forward-looking considerations as the virus continues to evolve, as well as anticipating what may be needed in a post-pandemic setting.”
Interim data from a Phase II trial of the Covid-19 vaccine revealed high neutralising antibody response rates across all adult age groups, with seroconversion rates of 95% to 100%.
A single vaccination led to high neutralising antibodies in subjects who had previous Covid-19 infection. This is said to indicate the vaccine’s potential as a booster dose.
Sanofi and GSK are planning to soon study their vaccine’s ability to stimulate a strong booster response, irrespective of the initial vaccine received.
Subject to Phase III results and regulatory reviews, the vaccine is expected to obtain approval in the fourth quarter of this year.