Sanofi and GlaxoSmithKline (GSK) will very soon be taking their COVID-19 vaccine candidate to U.S. and European regulators as both a primary series and booster, touting its 58 percent efficacy against symptomatic disease as proof that the shot works in a world with multiple COVID-19 variants.

That’s a much lower efficacy rate than the 90 percent-plus protection offered by the Moderna and Pfizer-BioNTech vaccines. But those vaccines were tested in a largely pre-variant world, when the original Wuhan strain was predominant. New data suggest that they are considerably less effective against emerging variants of concern.

Officials from Sanofi and GSK stress that their vaccine candidate is the only one globally tested when multiple variants were raging — including Beta; Delta, which causes more severe disease; and the highly contagious Omicron.

“No other global phase 3 efficacy study has been undertaken during this period with so many variants of concern, including Omicron, and these efficacy data are similar to the recent clinical data from authorized vaccines,” said Thomas Triomphe, executive vice president, Sanofi Vaccines.

Booster data had been anticipated last year, but company officials announced in December that the results would be delayed while they evaluated it in participants who haven’t been infected with the coronavirus (DID, Dec. 16, 2021).

The companies jointly announced that the messenger-RNA (mRNA) vaccine was effective in two studies: the VAT02 booster trial and the VAT08 phase 3 primary series study. Full data will be released later this year, they said. However, the topline results were generally positive.

VAT08 tested two 10-microgram doses against placebo in more than 10,000 adults. The vaccine was formulated with the spike protein of the original Wuhan virus. The two-dose series was 100 percent effective against severe COVID-19 and related hospitalizations, and 75 percent effective against moderate or severe COVID-19 disease. Its efficacy against any symptomatic COVID-19 was on the low side, at 57.9 percent. However, the companies said, this was “in line with expected vaccine effectiveness in today’s environment dominated by variants of concern.”

The booster study was conducted in subjects who had received a full series of any of the approved mRNA or adenovirus vaccines, or the Sanofi/GSK candidate. The vaccine increased neutralizing antibodies by 18- to 30-fold.

It was even more effective as a booster in patients who had already received it as their primary series, the company said. In this group, neutralizing antibodies increased 84- to 153-fold compared to pre-boost levels.

The companies are now launching a phase 3 primary series study of a new formulation based on the B.1.351 (Beta) variant. The formula’s phase 2 data were encouraging, they said.

“In that trial, the COVID-19 vaccine candidate was administered to 722 adults to assess the safety, reactogenicity and immunogenicity of two doses, and to identify an optimal dosing for use as a booster,” the companies said. “Results showed strong rates of neutralizing antibody response with 95-100 percent seroconversion following a second injection in all age groups [18-95 years old] across all doses.”

The companies also stressed that their candidate vaccine is stable at normal refrigerator temperatures — a bonus for distribution in regions with poor medical infrastructure. — Michele G. Sullivan