The so-called bivalent vaccine targets the Beta variant - first identified in South Africa - as well as the original Wuhan strain of the virus.
In a trial involving 13,000 adults, the vaccine demonstrated an efficacy rate of 64.7% against symptomatic COVID, and 72% efficacy against infections specifically caused by the Omicron variant.
When used in people who previously had COVID, the results were stronger. The vaccine generated an efficacy rate of 75.1% against symptomatic COVID and 93.2% in Omicron-confirmed symptomatic cases, the companies said.
"Sanofi-GSK's vaccine is the first candidate to demonstrate efficacy in a placebo-controlled trial in an environment of high Omicron variant circulation," Sanofi said in a statement.
Sanofi's Paris-listed shares and GSK's London-listed shares were both up more than 1% in morning trading.
Earlier this month, the bivalent vaccine showed potential in two trials to protect against the virus' main variants of concern - the Omicron BA.1 and BA.2 strains - when used as a booster shot.
Sanofi and GSK, two of the world's biggest vaccine makers, are hoping to gain a foothold in the market for next-generation variant-focused COVID shots, after falling behind competitors including Moderna, AstraZeneca and Pfizer-BioNTech, in the original race to contain the pandemic.
The new data supporting the bivalent vaccine will be submitted to regulatory authorities with the hope of making the shot available later this year, the companies said on Friday.
Sanofi and GSK's original COVID vaccine is already under review by the European Medicines Agency.
The companies have bet that this bivalent vaccine moulded on the now-supplanted Beta variant will confer broad protection against future viral strains on the basis that Beta expresses similar mutations across multiple variants of concern, including Omicron.
(Reporting by Tassilo Hummel in Paris nd Natalie Grover in London; Editing by Clarence Fernandez and Edmund Blair)
By Natalie Grover