"Sanofi and GSK announce a delay in their adjuvanted recombinant protein-based COVID-19 vaccine programme to improve immune response in older adults," a statement said, adding that the vaccine's potential availability had been pushed back "from mid-2021 to Q4 2021".
Trial results, Sanofi said, showed "an immune response comparable to patients who recovered from COVID-19 in adults aged 18 to 49 years, but a low immune response in older adults likely due to an insufficient concentration of the antigen."
The news also comes as a disappointment for a group of vaccines under development that rely on more conventional proven designs, as Britain begins rolling out the jab developed by German company BioNTech and their US partners Pfizer .
'Expect the unexpected' as vaccinations begin
Phase III studies postponed
Phase III studies were expected to start this month. Sanofi said it would launch a phase 2b study in February of next year instead. "The study will include a proposed comparison with an authorized COVID-19 vaccine," Sanofi said.
Both companies said they had "updated governments and the European Commission where a contractual commitment to purchase the vaccine has been made."
Sanofi and GSK would have been the fourth player to embark on Phase III studies on potential vaccines as governments struggle to quell the pandemic, which has killed more than 1.5 million people. The Phase I/II study tested the safety, tolerability and immune response of the vaccine in 440 healthy adults across 11 sites in the United States.
Despite the delay, Sanofi and GSK have boosted manufacturing in order to be ready to produce up to one billion doses of their vaccine in 2021.
This week, Britain began the world's first vaccine rollout, while Canada also approved the shot for use. Meanwhile, the US regulator is considering the BioNTech-Pfizer vaccine for approval. Rival developers AstraZeneca Plc and Moderna have also reported late stage data that shows their shots are effective in preventing the virus.