Sanofi and GlaxoSmithKline said on Wednesday a single booster dose of their COVID-19 vaccine candidate provided strong immune responses, preliminary data from clinical trials show, a boost for the drugmakers after lagging the vaccine race.

The French and British partners said they expected more results of the late-stage Phase III study of their recombinant adjuvanted COVID-19 vaccine candidate in the first quarter.

They plan to file booster data with regulatory authorities following the Phase III results.

"The booster was well tolerated, with a safety profile similar to currently approved COVID-19 vaccines. This is the most comprehensive booster trial to date to explore boosting across different vaccine technologies used for primary vaccination", the companies said in a statement.

"To provide the necessary data to regulatory authorities for the booster vaccine submission, the trial will continue to accrue the number of events needed for analysis, with results expected in Q1, 2022."

No safety concerns were identified.

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

The news provides some optimism for the companies after falling behind rivals in the race for COVID-19 shots and big delays with the development of this shot.

Last year, trials for the shot showed an insufficient immune response in older people. The companies had said the vaccine could be approved by the year-end after initially targeting the first half of the year.

At the end of September, Sanofi dropped its plans for its own mRNA-based COVID-19 vaccine because of the dominance achieved by BioNTech-Pfizer and Moderna in using the technology to fight the pandemic.


The booster shot has been tested for all age groups and for people who have received four of the most widely approved shots - AstraZeneca, Johnson & Johnson, Moderna and Pfizer/BioNTech - as part of their primary vaccine.

It was administered between four and ten months after a complete primary vaccination schedule. The Omicron variant was not circulating during the trial.

"Preliminary results from the VAT0002 clinical trial investigating the safety and immunogenicity of the booster showed neutralizing antibodies increased nine to 43-fold regardless of the primary vaccine received (AstraZeneca, Johnson & Johnson, Moderna, Pfizer/BioNTech) and for all age groups tested", Sanofi said.

The company said this was the most "comprehensive" booster trial to date as European countries grapple with a new wave of COVID-19 infections fuelled by the Delta variant of the virus and are gearing up for the new more contagious Omicron variant.

Sanofi also it was continuing "its contribution to global public health needs" with the manufacturing of up to half a billion doses from BioNTech/Pfizer, Moderna, and Johnson & Johnson vaccines.