An Overview of the Sanofi/GSK COVID-19 Vaccine

Sanofi Pasteur and GlaxoSmithKline were expecting to start a Phase 3 clinical trial for a vaccine to fight the novel coronavirus (COVID-19) in December 2020. Instead, the Phase 3 trial launched in May 2021 after the pharmaceutical companies went back to the lab to rework the formula and conducted a redo of the second phase of the clinical trials.

The combined effort between the two companies had Sanofi developing a vaccine using an adjuvant from GlaxoSmithKline (GSK). The companies revised plans for the Phase 2 trial of the vaccine after the initial results weren't what they had hoped.

In May 2021, the companies announced that their amended protein-based recombinant vaccine showed a strong antibody response across all age groups in a Phase 2B clinical trial that included 722 participants ages 18 to 95. The vaccine also showed a strong immune response in patients with prior COVID-19 infection, which suggests it may have potential as a booster vaccine, according to Sanofi and GSK.

Pending results from the Phase 3 trial, the companies hope to have the vaccine considered for regulatory approval by the end of 2021.

How It Works

The Sanofi/GSK vaccine candidate is a recombinant protein-based vaccine based on the baculovirus, which is commonly found in moths. Pieces of the novel coronavirus are used in combination with the baculovirus to effectively program the immune system to better recognize and fight COVID-19. There are a number of other recombinant vaccines in development from other pharmaceutical companies.

Sanofi is working on a second type of COVID-19 vaccine, too. The second effort involves a messenger RNA (mRNA) vaccine (the delivery method for the Pfizer and Moderna vaccines), which uses strands of genetic material to teach the immune system new strategies to recognize and fight disease. This vaccine is in partnership with the mRNA therapeutics company Translate Bio and is in the early stages. Sanofi announced on March 12, 2021 that it had started a Phase 1/2 clinical trial that will enroll about 415 adults. Preliminary results are expected in the summer.

How Effective Is It?

In May 2021, Sanofi and GSK announced that preliminary results from the Phase 2B trial using the amended formula showed that the vaccine achieved comparable antibody levels to people who had COVID-19 and developed antibodies naturally. This was across all age groups, though antibody levels were higher within the 18 to 59 age group than the 60 and older age group.

In initial, early-stage trials, Sanofi reported that the company's recombinant vaccine achieved similar antibody levels as those found in people aged 18 to 48 who'd had COVID-19. In older adults above age 48, however, the vaccine underperformed. In that group, the antibody levels generated by the vaccine were less than in people with natural immunity.

After reviewing these early-stage results, Sanofi/GSK requested approval for a Phase 2B trial. The companies have tested a number of combinations of one and two doses of vaccine, as well as different adjuvants.

The companies want to test the reformulated vaccine against another authorized vaccine rather than a placebo. According to Sanofi, when tested in animals, the reformulated vaccine has been shown to protect the lungs against the damage COVID-19 causes.

When Will It Be Available? 

Research on the vaccine has been delayed by the need for reformulation, but the Phase 2B trial plan was approved in February 2021 and preliminary results were announced in March. Now, Sanofi and GSK are planning for the next phase of testing. This means that, if the Phase 3 trial proceeds smoothly, regulatory approval likely would come in the fourth quarter of 2021.

Who Can Get the Sanofi/GSK Vaccine?

Sanofi and GSK are working on developing vaccines for adults at the moment, with no word yet on when testing will begin in children and teen populations.

Once the vaccine is available, any doses purchased by the U.S. government will be free to U.S. citizens. The facility or agency that offers the vaccine may submit for reimbursement from health insurance, but the provider cannot charge any fees to the person receiving the vaccine, including those without insurance.

Side Effects and Adverse Events

Full results of the Phase 2B trial haven't been published yet, but Sanofi says there were no safety concerns in the more than 400 people who participated in the first studies or in the 722 people who participated in the Phase 2B trial. Additional information will be provided as trials advance with the new formulation of the vaccine. No information on side effects has been released yet for Sanofi's mRNA vaccine.

Funding and Development

Sanofi and GSK are developing the recombinant vaccine with the help of government funding. In July 2020, the partnership was awarded $30 million through a program administered by the U.S. Department of Health and Human Services called the Biomedical Advanced Research and Development Authority (BARDA) and Operation Warp Speed.

BARDA is awarding the funds in an effort to speed up how quickly vaccines to fight COVID-19 can be developed and approved for use. The agreement entitles the U.S. government to 100 million doses of the vaccine if approved, with another $2 billion in funds available for another 500 million doses if the government decides to exercise its option for those additional doses.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.