Preliminary Data Suggest GSK, Sanofi COVID-19 Booster Effective Regardless of Initial Vaccine


A single booster dose of the GlaxoSmithKline and Sanofi recombinant adjuvanted COVID-19 vaccine candidate delivered consistent and strong immune responses.

A single booster dose of the GlaxoSmithKline (GSK) and Sanofi recombinant adjuvanted COVID-19 vaccine candidate delivered consistent and strong immune responses regardless of the primary vaccine received, according to the preliminary results of the VAT0002 trial. The booster was also well-tolerated, with a safety profile similar to currently approved COVID-19 vaccines.

According to the company, this is the most comprehensive booster trial to date to explore boosting across different vaccine technologies used for primary vaccination.

“As the pandemic threat continues with the current dominant Delta variant and Omicron rapidly gaining ground, booster vaccines will continue to be needed to help protect people over time,” said Roger Connor, president of GSK Vaccines, in a press release. “The initial booster data are promising, and we await the phase III results to determine the next steps on making protein-based adjuvanted COVID-19 vaccines available."

The preliminary results of the trial found that neutralizing antibodies in individuals given the booster increased 9- to 43-fold regardless of the primary vaccine received. The trial also includes regular reviews by an independent data safety monitoring board (DSMB). The DSMB identified no safety concerns in its last review and recommended the continuation of the trial into early 2022 to accrue more data.

“These preliminary data show we have a strong booster candidate, whatever primary vaccine you have received,” said Thomas Triomphe, executive vice president, Sanofi Pasteur, in the release. “This is consistent with our efforts to provide relevant responses to evolving public health needs. While pursuing a phase 3 trial is a challenge in a quickly shifting pandemic environment, we look forward to seeing the results to support submissions of our booster vaccine as quickly as possible.”

Regulatory authorities require phase 3 efficacy to be demonstrated in naïve populations, meaning that participants must be seronegative with no history of COVID-19 infection. The trial recruited the majority of its participants in Q3 2021, which coincided with a significant increase in the number of people infected by the COVID-19 virus globally due to the Delta variant.

The trial will continue to accrue the number of events needed for analysis to provide the necessary data to regulatory authorities. Results of the study are expected in Q1 2022.


GSK and Sanofi announce positive preliminary booster data for their COVID-19 vaccine candidate and continuation of phase III trial per independent Monitoring Board recommendation [news release]. GSK; December 15, 2021. Accessed December 15, 2021.

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