PARIS, June 13 (Reuters) - French drugmaker Sanofi said on Monday an upgraded version of the COVID-19 vaccine candidate it is developing with GSK showed potential in two trials to protect against the virus's main variants of concern, including the Omicron BA.1 and BA.2 strains, when used as a booster shot.

While the two companies' first experimental COVID shot is undergoing review by the European Medicines Agency, Sanofi and GSK have continued work on a vaccine that is molded on the now-supplanted Beta variant, hoping still that it will confer broad protection against future viral mutations.

Sanofi said this new vaccine candidate was shown to significantly boost antibody levels against a number of variants of concern, when given to trial participants who had an initial course of mRNA vaccines, a type made by BioNTech-Pfizer and Moderna.

In a separate trial conducted by a French hospitals network, Sanofi's Beta-adapted booster shot triggered a higher immune response than Sanofi's first-generation shot or Pfizer-BioNTech's established vaccine in previously vaccinated volunteers. "The Beta variant expresses similar mutations across multiple variants of concern, including Omicron, making it a strong vaccine candidate to confer broad protection against multiple strains of COVID-19," said Thomas Triomphe, the head of Sanofi's vaccine business.

Highlighting the need for vaccine makers to address new variants of concern in a saturated COVID vaccine market, Valneva on Friday said it was in talks to try and salvage a supply agreement that the European Commission cancelled.

Valneva's product is based on the original virus found in the Chinese city of Wuhan, like BioNTech-Pfizer and Moderna's dominant first-generation shots.

(Reporting by Ludwig Burger in Frankfurt, Tassilo Hummel in Paris; Editing by Tom Hogue and Emelia Sithole-Matarise)