A Covid-19 vaccine candidate developed by Sanofi and US group Translate Bio "will not be ready this year," the French drugmaker's chief executive told Le Journal du Dimanche newspaper.
Clinical trials of this vaccine, which will be based on a technology known as mRNA -- on which lean approved vaccines of Pfizer/BioNTech and Moderna --, are expected to start this quarter.
In December last year, Sanofi had said it was targeting "earliest potential approval" of the shot in the second half of 2021, following positive preclinical data.
"This vaccine will not be ready this year, but it could be of use at a later stage all the more if the fight against variants was to continue," Paul Hudson was quoted as saying.
The CEO gave no other details. Officials at Sanofi were not available for comment.
The news could mark another blow for Sanofi, already embattled with a delay for another Covid-19 vaccine candidate it hopes to bring to patients and for which the company has teamed up with Britain's GlaxoSmithKline.
The two groups stunned investors last year by warning their traditional, protein-based Covid-19 jab showed an insufficient immune response in older people, delaying its launch towards the end of 2021.
To appease critics, Sanofi said last month it had agreed to fill and pack millions of doses of the Pfizer/BioNTech vaccine from July.
Some 108 million people have been reported to be infected by the novel coronavirus globally and more than 2.4 million have died since first cases were identified in China in December 2019, according to a Reuters tally.
Countries worldwide have since the beginning of the year embarked on mass vaccination programmes, with mixed results, and are now confronted with the emergence of several variant strains which forces them to move even more quickly.