Sanofi suffers major setback in development of a Covid-19 vaccine

One of the world’s leading vaccine manufacturers has suffered a major setback in its work to produce a Covid-19 vaccine. The problem will push the timeline for deployment of Sanofi Pasteur’s vaccine — if it is approved — from the first half of 2021 into the second half of the year, the company said Friday.

The news is not just disappointing for Sanofi and its development partner, GlaxoSmithKline, which is providing an adjuvant used in the vaccine. The companies have contracts with multiple countries, including the United States and Britain, as well as the European Union.

Sanofi had hoped to start a Phase 3 trial of the vaccine this month and had projected it could produce 100 million doses of vaccine in 2020, and 1 billion doses in 2021.


The problem relates to inadequate results in older adults in Sanofi’s Phase 1/2 trial, which the company traced back to an inadequate formulation of their vaccine, Su-Peing Ng, global medical head for Sanofi Vaccines, told STAT in an interview.

Ng said both Sanofi and GSK are committed to continuing work on the vaccine, and plan to begin a Phase 2b trial in February.


“We’re disappointed that there is a delay,” she said. “I think, though, that we’re encouraged that we have enough information, enough of the results from preclinical and clinical [studies] to tell us that we have a path forward. We need to optimize this formulation.”

In effect, participants in the trial received too little vaccine. While the too-small dose generated adequate levels of neutralizing antibodies in adults aged 18 to 49 in the trial, adults 60 and older generated lower levels of neutralizing antibodies than are seen in the blood of people who have recovered from Covid-19 infection, Ng said.

Perplexed by the findings, the company set out to figure out why the vaccine underperformed. It discovered two commercial reagents used to measure how much antigen — active vaccine — was included in each dose were giving false readings. In fact, Ng said, the concentration of the antigen “was insufficient.”

A revised formulation, tested recently in non-human primates, showed the vaccine prevented damage in the lungs, which is what triggers severe Covid disease in people, and led to rapid clearance of the virus.

The vaccine’s path will be more challenging because of this delay; the Covid vaccine landscape is changing daily and placebo-controlled trials may not be feasible for much longer, with the first vaccines soon to be deployed. If people know they may soon have access to an authorized vaccine, there is less motivation to enroll in a trial where they might get a placebo.

Sanofi knows this and is proposing to the Food and Drug Administration that its Phase 2b trial compare its vaccine to one that is already authorized, not a placebo.

“To continue to provide confidence that we’re going to have a vaccine that meets the expected standard of care, we propose the comparison with an authorized Covid-19 vaccine instead of placebo control,” Ng said.

That would set a very high bar for the Sanofi vaccine. Pfizer and Moderna, the front-runners in the vaccine race, have reported vaccine efficacy of about 95% in their Phase 3 trials. If the Sanofi vaccine doesn’t reach that level of efficacy, can it be brought to market, STAT asked Ng.

“That will be up to the regulators,” she said, adding that “for the public to be confident in the choice of a vaccine, it would have to be pretty close to what’s been established now.”

The Sanofi vaccine would have one advantage compared to the Pfizer and Moderna vaccines: It wouldn’t require ultracold storage and could instead be kept in standard refrigerators, making it easier to distribute.

Pfizer and Moderna are poised to receive emergency use authorizations from the FDA this month — an FDA advisory panel endorsed the Pfizer shot on Thursday — and vaccine rollout in the United States is expected to begin within days of the FDA’s green light. The Phase 3 trial for Johnson & Johnson’s vaccine — the only one-dose vaccine currently in clinical trials in the U.S. — is about to finish enrollment; if it is effective, it could get an EUA in the first quarter of 2021.

The Sanofi vaccine is made with an approach the company uses for one of its flu vaccines, Flubok. That in theory is an advantage; the FDA knows how this vaccine system works. It’s called a recombinant protein vaccine, with the spike protein of the SARS-CoV-2 virus, which cases Covid-19, generated in insect cells.

Sanofi is also developing a second vaccine, a messenger RNA vaccine, like the Pfizer and Moderna shots. For this project, it is collaborating with Translate Bio, a Lexington, Mass.-based biotech. Clinical trials for that vaccine have not yet begun.

Source: STAT