An experimental COVID-19 vaccine developed by French drugmaker Sanofi and Britain's GlaxoSmithKline showed an insufficient immune response in clinical trial results, Sanofi says.
The two companies plan to launch another study next year, hoping to come up with a more effective vaccine by the end of 2021.
The news comes as a disappointment for a crop of vaccines under development that rely on more conventional proven designs, as the shot developed by Pfizer and BioNTech using breakthrough technology gets rolled out across Britain.
Friday's 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".
Phase three studies were expected to start this month.
Sanofi said it would launch a phase 2b study in February of next year instead, after a recent challenge study in non-human primates using an improved antigen formulation demonstrated better effects.
"The study will include a proposed comparison with an authorised COVID-19 vaccine," the company said.
"If data are positive, a global Phase III study could start in Q2 2021. Positive results from this study would lead to regulatory submissions in the second half of 2021, hence delaying the vaccine's potential availability from mid-2021 to Q4 2021."
The two companies said they had "updated governments and the European Commission where a contractual commitment to purchase the vaccine has been made."
The companies would have been the 14th player to embark on Phase three studies on potential vaccines as governments struggle to tame the pandemic that has killed more than 1.5 million people, according to World Health Organization records.
This week, Britain started deploying a vaccine that uses a breakthrough mRNA technology developed by Pfizer and BioNTech, jumping ahead of the rest of the world in the race. Canada gave the green light for the shot, too.
The data comes as the US regulator considers the Pfizer-BioNTech vaccine for approval.
Rival developers AstraZeneca and Moderna have also reported late stage data that shows their shots are effective at preventing the virus.
The French group is also working on another vaccine candidate to prevent COVID-19 with US company Translate Bio, which will rely on a different technology called mRNA, similar to the developed by Pfizer and Moderna.
Phase one trials for this vaccine are expected to start this month.
Australian Associated Press