After setback, Sanofi, GSK take tweaked COVID-19 vaccine into phase 2

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If all goes to plan, Sanofi and GSK will file for approval in the second half of the year. (Getty Images/Naeblys)

Sanofi and GlaxoSmithKline have begun a phase 2 clinical trial of a new version of their adjuvanted recombinant protein-based COVID-19 vaccine candidate. The study start comes around two months after weak clinical data forced the partners to rethink the antigen formulation.

In last year’s phase 1/2 clinical trial, the original formulation of the Sanofi-GSK vaccine failed to trigger the desired immune response in adults aged 50 years and older. The setback, which followed stellar phase 3 data on rival vaccines, prompted Sanofi and GSK to go back to the laboratory in an effort to come up with a more effective candidate.

Sanofi and GSK are now ready to find out whether the new formulation performs better in humans. The phase 2 clinical trial will enroll 720 adults, split evenly between those aged under and over 60 years, and randomize them to receive one of three antigen doses. The adjuvant dose is the same in all three cohorts. 

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Based on the data, Sanofi and GSK will design a phase 3 clinical trial that is scheduled to start in the second quarter. If all goes to plan, Sanofi and GSK will file for approval in the second half of the year and be in a position to start providing commercial doses by the end of 2021. The partners originally aimed to make their vaccine available around the middle of 2021.

The delay means the vaccine is unlikely to play a significant role in the first round of vaccinations in Western countries. U.S. President Joe Biden is aiming to have enough doses of other vaccines to protect all Americans by the end of July. U.K. Prime Minister Boris Johnson set the same deadline for offering every adult in the U.K. their first vaccine dose.

Vaccines from AstraZeneca, Johnson & Johnson, Moderna, Novavax and Pfizer-BioNTech look set to make those targets achievable. Yet, Sanofi and GSK could still play a role in the longer-term control of the coronavirus. 

Notably, Sanofi and GSK’s adjuvanted protein-based technology could be better suited to protecting people against multiple circulating variants than other platforms. The virus-based approaches used by AstraZeneca and J&J may confer vector immunity that limits the effectiveness of repeat dosing. Equally, Moderna and Pfizer-BioNTech may struggle to provide protection against multiple variants in a single vaccine without causing levels of immune stimulation that make tolerability an issue.

Sanofi and GSK, in contrast, can potentially keep levels of immune stimulation constant—by using the same dose of adjuvant—while including additional antigens to protect against multiple variants in a single vaccine. Novavax’s near-approval COVID-19 vaccine is based on similar technology.

Like Novavax, Sanofi is working on vaccines to protect against coronavirus variants. Clinical data on other COVID-19 vaccines suggest the existing Sanofi-GSK asset is likely to be less effective against the B.1.351 variant first identified in South Africa. By the time Sanofi and GSK get to market, Western countries may have protected their populations against the original coronavirus and be focused on jabs against variants such as B.1.351.