The European Union's drug regulator has started reviewing Sanofi and its British partner GlaxoSmithKline's application seeking conditional authorization for their COVID-19 vaccine, the agency said on Wednesday.

The drugmakers had earlier said that they would seek regulatory approval for their COVID-19 vaccine to be used as a booster as well as a standalone two-dose shot.

The vaccine candidate, Vidprevtyn, was already being evaluated under a rolling review by the European Medicines Agency (EMA).

Sanofi, which plans to produce the vaccine in France, Italy and the United Sates, is hoping for a comeback after falling behind in the race for COVID-19 shots, while GSK, the world's biggest vaccine maker by sales, has not developed its own candidate and is instead contributing its adjuvant technology to developers.

Vidprevtyn uses the same technology as one of Sanofi's seasonal influenza vaccines, which is then coupled with an adjuvant, a substance that acts as a booster to the shot, made by GSK.

(Reporting by Mrinalika Roy in Bengaluru; Editing by Saumyadeb Chakrabarty)