Sanofi and GlaxoSmithKline (GSK) have reported strong immune responses with their adjuvanted recombinant Covid-19 vaccine candidate in Phase II clinical trial.

In all adult age groups participating in the trial, the neutralising antibody response rates were comparable to those observed in people who have recovered from the disease.

The randomised, double-blind, multi-centre, dose-ranging trial involved healthy individuals aged 18 years and above, including people with high-risk medical conditions. Since February this year, the trial recruited 722 subjects in the US and Honduras.

It assessed the safety, reactogenicity and immunogenicity of two doses of the vaccine administered 21 days apart, with antigen dose levels of 5µg, 10µg, and 15µg.

Across all doses, interim data revealed 95% to 100% seroconversion rates after the second injection in subjects aged 18 to 95 years. Tolerability of the vaccine was acceptable without any safety concerns, the companies said.

Furthermore, a single injection led to high levels of neutralising antibodies in people who previously had Covid-19, indicating the potential for advancing as a booster vaccine.

Sanofi Pasteur executive vice-president and global head Thomas Triomphe said: “Our Phase II 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.

“We look forward to generating additional data and working with our partners around the world to make our vaccine available as quickly as possible.”

Based on these Phase II data, the companies will launch a global, randomised, double-blind Phase III trial in the coming weeks. The Phase III study will assess the vaccine’s 10µg dose plus GSK’s pandemic adjuvant in more than 35,000 adult volunteers.

Sanofi and GSK will also perform studies to evaluate the potential of the vaccine’s lower dose to induce a strong booster response. The vaccine is anticipated to secure approval in the fourth quarter of this year.

In September last year, the companies launched a Phase I/II clinical trial to evaluate their vaccine.