Weak clinical data force Sanofi, GSK to delay COVID-19 vaccine

sanofi quebec hq
Sanofi's headquarters in Quebec (Sanofi)

Sanofi and GlaxoSmithKline’s COVID-19 vaccine has failed to trigger the desired immune response in people aged 50 years and older, forcing the partners to rethink the antigen formulation. The setback is expected to delay the availability of the vaccine from mid-2021 to near the end of next year.

Using an adjuvant from GSK, Sanofi developed a recombinant protein-based COVID-19 vaccine. The approach took longer than the creation of mRNA and viral vectored vaccines but offered potentially better results due to its combination of established vaccine technologies. That hypothesis took a hit Friday when Sanofi and GSK shared an update on the program.

Interim data from a phase 1/2 trial showed the vaccine triggered immune responses in people aged 18 to 49 years that were comparable to those seen in convalescent COVID-19 patients. However, Sanofi and GSK saw “a low immune response” in older adults.

Sanofi and GSK have identified an insufficient concentration of the antigen as the likely cause of the weak data. That thinking is supported by a recent challenge study of a new antigen formulation in nonhuman primates, which found the vaccine protected against lung pathology and supported viral clearance from the nasal passages and lungs in two to four days.

The data encouraged Sanofi and GSK that their technologies can form the basis of an effective shot despite the shortcomings of the formulation tested in the phase 1/2. In light of the data, Sanofi and GSK are rethinking their strategy.

Having planned to move the original formulation into phase 3 this month, the partners now expect to start a phase 2b of a new antigen formulation in February. The trial will compare the experimental prophylactic to an authorized COVID-19 vaccine. As a result of the delay, Sanofi and GSK have pushed back the targeted launch from mid-2021 to the fourth quarter of next year.

Analysts at Jefferies said the delay may prove an opportunity to other companies. “This delay pushes the anticipated launch of Sanofi/GSK's vaccine further back in the pack of competitors. JNJ recently announced it expects to submit an EUA application for its single dose adenovirus vaccine in February 2021E. The delay also provides an opportunity for Novavax's protein vaccine NVX-CoV2373 as interim data from its UK Phase III trial are expected as early as 1Q21E, with these data expected to serve as the basis for licensure applications,” the analysts wrote.

The news is a blow to the global response against the coronavirus. Sanofi and GSK planned to make up to 1 billion doses next year and were central to the vaccination programs of multiple countries. The European Commission secured up to 300 million doses of the vaccine. The U.S. has an initial agreement for 100 million doses, plus an option to buy up to 500 million more. The U.K. has lined up a deal for 60 million doses, and Canada has ordered 72 million shots. 

With Sanofi and GSK bringing their manufacturing might to bear on the projects, the partners could serve those Western markets and still have doses available for other regions. Sanofi and GSK agreed to provide 200 million doses to the COVAX Facility set up to facilitate equitable access to vaccines. As a candidate that is stable at temperatures used for routine vaccines, the vaccine is better suited for use in large parts of the world than prophylactics from Moderna and Pfizer.