Sanofi and GSK will test their two-dose SARS-CoV2 vaccine candidate as a booster for other vaccines during its phase 3 trial, following a phase 2 trial that showed that it triggered a strong neutralizing antibody response in people previously vaccinated.

Those who had already been vaccinated showed a strong response after one jab, indicating that that the candidate vaccine could be used as a “booster” shot against variants, according to a press statement from Sanofi on Monday.

The as-yet-unpublished results showed “95% to 100% seroconversion following a second injection in all age groups (18 to 95 years old) and across all doses, with acceptable tolerability and with no safety concerns,” according to Sanofi.

The phase 2 trial, which started in February in the US and Honduras, consisted of 722 volunteers split equally between those aged 18 to 59 year-olds and those 60 years and above.

The adjuvanted recombinant vaccine is based on one of Sanofi’s seasonal influenza vaccines in combination with GSK’s pandemic adjuvant, and it targets the SARS-CoV2 virus spike protein.

“Our phase 2 data confirm the potential of this vaccine to play a role in addressing this ongoing global public health crisis, as we know multiple vaccines will be needed, especially as variants continue to emerge and the need for effective and booster vaccines, which can be stored at normal temperatures, increases”, said Thomas Triomphe, Executive Vice President and Global Head of Sanofi Pasteur on Monday. 

‘Shows Potential to Address Variants’

GSK president Roger Connor added that the data showed “the potential of this protein-based adjuvanted vaccine candidate in the broader context of the pandemic, including the need to address variants and to provide for booster doses”. 

The companies intend to start a phase 3 trial “as soon as possible to meet our goal of making it available before the end of the year”, added Connor.

Around 35,000 people will be enrolled in the phase 3 trial, which will include “booster studies with various variant formulations in order to assess the ability of a lower dose of the vaccine to generate a strong booster response regardless of the initial vaccine platform received,” according to the media release.

Booster shots may be necessary to address new virus variants that are able to escape the neutralising antibodies of earlier vaccines.

Results of the Novavax vaccine, published in Nature in March, support this concern. The vaccine was 90% effective against the UK-identified B1.17 variant but only 49.4% effective against the B1.351 variant first identified in South Africa. Newer variants identified in Brazil and India have not yet been tested against vaccines.

But Columbia University Professor David Ho, the Novavax study’s lead author, said that his study and other data showed that “the virus is traveling in a direction that is causing it to escape from our current vaccines”. 

“If the rampant spread of the virus continues and more critical mutations accumulate, then we may be condemned to chasing after the evolving SARS-CoV-2 continually, as we have long done for influenza virus,” Ho said in an interview. 

Image Credits: International Monetary Fund/Ernesto Benavides.