Sanofi-GSK COVID-19 Vaccine Hits Snag With Insufficient Immune Response in 50+ Population

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The COVID-19 vaccine candidate developed by Sanofi and GlaxoSmithKline hit a snag that will delay the launch of a Phase III study due to an insufficient immune response in older trial patients. The vaccine will now not be available until the end of 2021 – if at all.

This morning, Sanofi said interim results of its Phase I/II vaccine study showed an immune response comparable to patients who recovered from COVID-19 in adults aged 18 to 49 years. However, in adults 50 and above, there was an “insufficient immune response.” Sanofi that it will have to refine the concentration of antigen in order to provide high-level immune response across all age groups.

Instead of a Phase III trial, Sanofi said it will plan a Phase IIb study with an improved antigen formulation. The study, which is supported by Biomedical Advanced Research and Development Authority (BARDA), is expected to begin in February, Sanofi said. The study will include a proposed comparison with an authorized COVID-19 vaccine. If data are positive, a global Phase III study could start in the second quarter of 2021 and, if that proves to be positive, Sanofi said its vaccine could be available by the fourth quarter of 2021.

The disclosure comes the same day the U.S. food and Drug Administration is expected to grant Emergency Use Authorization to a vaccine candidate developed by Pfizer and BioNTech. A vaccine candidate developed by Moderna could receive EUA as early as next week following a review of safety and efficacy data.

The vaccine candidate uses Sanofi’s S-protein COVID-19 antigen, which is based on recombinant DNA technology to develop the vaccine candidate. That antigen will be boosted by GSK’s pandemic adjuvant technology. Sanofi had been expected to release the results from the Phase I/II clinical trial that launched in September later this month and begin the Phase III study. Full results of the Phase I/II study will be published as soon as all data are available, following peer-reviewed publication process.

The vaccine candidate uses the same recombinant protein-based technology as one of Sanofi’s seasonal influenza vaccines and GSK’s pandemic adjuvant technology. Sanofi’s S-protein COVID-19 antigen, which is based on recombinant DNA technology to develop the vaccine candidate. That antigen will be boosted by GSK’s pandemic adjuvant technology. The use of an adjuvant may reduce the amount of vaccine protein required per dose, which allows more vaccine doses to be produced and protect more people.

Thomas Triomphe, head of Sanofi Pasteur, expressed his disappointment in the delay.  

“We care greatly about public health which is why we are disappointed by the delay announced today, but all our decisions are and will always be driven by science and data. We have identified the path forward and remain confident and committed to bringing a safe and efficacious COVID-19 vaccine. Following these results and the latest encouraging new preclinical data, we will now work to further optimize our candidate to achieve this goal,” Triomphe said in a statement.

A recent challenge study in non-human primates performed with an improved antigen formulation demonstrated that the vaccine candidate could protect against lung pathology and lead to rapid viral clearance from the nasal passages and lungs, within 2 to 4 days. These results increase the companies’ confidence in the capacity of the adjuvanted recombinant platform to deliver a highly efficient vaccine for all adults.

In addition to the recombinant protein-based vaccine in collaboration with GSK, Sanofi is developing a messenger RNA vaccine in partnership with Translate Bio. Preclinical data showed that two immunizations of the mRNA vaccine induced high neutralizing antibody levels that are comparable to the upper range of those observed in infected humans. Sanofi expects the Phase I/II study to begin in the first few months of 2021.

Sanofi and GSK said they have notified the various governments they have supply deals with of the delay, including a $2.1 billion deal with the U.S. government for 100 million doses of the vaccine.

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