The companies say they are in discussions with regulatory authorities, including the US Food and Drug Administration (FDA) and European Medicines Agency (EMA), and plan to submit the data to support regulatory authorizations: although it has not given a timeline for doing so.
The vaccine is being tested in two trials: one Phase 3 trial using the vaccine as a primary series of two doses, pitted against variants such as Omicron; and the second using the vaccine as a booster after initial mRNA or adenovirus vaccinations.
The companies champion the advantages of the adjuvanted protein-based vaccine, using a well-established approach that has already been applied to other viruses including pandemic flu, and which can be stored at refrigerated temperatures.
Phase 3 data
In the two-dose primary series Phase 3 trial (VAT08), the vaccine demonstrated:
- 100% efficacy against severe COVID-19 disease and hospitalizations;
- 75% efficacy against moderate or severe COVID-19 disease;
- 57.9% efficacy against any symptomatic COVID-19 disease (the companies say this is in line with expected vaccine effectiveness against today’s variants of concern).
Sanofi and GSK partnered up early in the pandemic to develop the vaccine, using Sanofi's recombinant antigen and GSK's pandemic adjuvant. The project, however, suffered a setback at the end of 2020 with the initial candidate failing to generate a sufficient immune response in older people.
A refined antigen formulation entered Phase 2 trials in February 2021, with interim results showing high rates of neutralizing antibody responses in all adult age groups. Phase 3 trials started in May last year.
New data from Sanofi and GSK released today states that, in participants who had received a primary series of an already authorized mRNA or adenovirus vaccine, the Sanofi-GSK booster vaccine ‘induced a significant increase in neutralizing antibodies of 18- to 30-fold across vaccine platforms and age groups’.
When the vaccine was used as a two-dose primary series followed by a booster dose, neutralizing antibodies increased 84- to 153-fold compared to pre-boost levels.
When used as a two-dose primary series, the Sanofi-GSK vaccine delivered robust levels of neutralizing antibodies, with GMTs reaching 3711 units (For comparison, a panel of sera from volunteers who received two doses of an approved mRNA vaccine displayed a GMT of 1653 units).
Across the studies, the Sanofi-GSK vaccine was well-tolerated in younger and older adults with no safety concerns.
Thomas Triomphe, executive vice president, Sanofi Vaccines, said: “We’re very pleased with these data, which confirm our strong science and the benefits of our COVID-19 vaccine. The Sanofi-GSK vaccine demonstrates a universal ability to boost all platforms and across all ages. We also observed robust efficacy of the vaccine as a primary series in today’s challenging epidemiological environment.
"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.”
Roger Connor, president of GSK Vaccines, added: “The evolving epidemiology of COVID-19 demonstrates the need for a variety of vaccines. Our adjuvanted protein-based vaccine candidate uses a well-established approach that has been applied widely to prevent infection with other viruses including pandemic flu.
"We are confident that this vaccine can play an important role as we continue to address this pandemic and prepare for the post-pandemic period.”
Phase 3 studies
VAT08 is evaluating a 10µg antigen formulation of the adjuvanted recombinant protein-based vaccine for efficacy, immunogenicity and safety compared to a placebo.
Stage one of the trial is assessing the efficacy of a vaccine formulation containing the spike protein against the original D614 (parent) virus in more than 10,000 participants >18 years of age, randomized to receive two doses of 10µg vaccine or placebo at day 1 and day 22 across sites in the US, Asia, Africa and Latin America.
Enrolment recently completed for a second stage in the trial, evaluating a second bivalent formulation, including the spike protein of the B.1.351 (Beta) variant.
VAT02 is a global booster trial.
Full study results for both VAT08 and VAT02 will be published later this year.