Sanofi’s long-delayed Covid-19 vaccine shows promise as booster

The data suggest that the shot could eventually be used in booster campaigns after it failed to fulfill initial expectations

Sanofi, the French pharmaceutical company, said Wednesday that its once highly anticipated Covid-19 vaccine produced strong immune responses in vaccinated volunteers who received a single dose of the shot as a booster.

The data suggest that the shot, which is still in development and not authorized anywhere in the world, could eventually be used in booster campaigns after it failed to fulfill initial expectations that it would become one of the most important weapons in the fight against the virus. Still, Sanofi has yet to finish a key clinical trial that it said would need to generate results before regulators around the world consider authorizing the shot.

Sanofi said that study participants who received the company’s shot as a booster saw large increases in their levels of neutralizing antibodies, which are one subset of the expansive immune response prompted by vaccines. The more than 500 volunteers had been fully vaccinated between four and 10 months earlier with either Johnson & Johnson’s single-shot vaccine or two shots of the vaccines from Pfizer, Moderna, or AstraZeneca.

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The antibody responses generated by using the Sanofi shot as a booster were comparable to those seen with a boost of the Pfizer shot in a separate study that compared seven different vaccine brands.

Sanofi said that laboratory testing is underway to see if the vaccine might work against the fast-spreading omicron variant. The company said that scientists are using blood samples from volunteers in the booster study to see how their vaccine-generated antibodies fare against the omicron variant.

Sanofi is still waiting for results from a large Phase 3 study that will assess the safety and efficacy of its vaccine. Those results were supposed to come in the latter part of this year. But Sanofi said Wednesday that too few volunteers in its trial have gotten sick with Covid, delaying the results until early next year.

In the past, the Food and Drug Administration has wanted to see results from Phase 3 trials on previously unvaccinated volunteers before considering a vaccine as a booster. But the agency has updated its requirements during the pandemic to bring vaccines more quickly into use.

Sanofi said in a news release that it planned to file its booster data with regulatory authorities after it has Phase 3 trial results.

Sanofi’s shot uses a more conventional approach than that deployed in other, more swiftly developed Covid vaccines. It triggers immunity using a version of the coronavirus’s spike protein that was synthesized in a laboratory using engineered viruses that grow inside insect cells. Sanofi led the development of the shot with help from GlaxoSmithKline, which supplied an adjuvant, an ingredient commonly used in vaccines meant to boost the immune response.

In the early months of the pandemic, the vaccine was one of six selected for funding from Operation Warp Speed, the Trump administration’s effort to accelerate vaccine development.

But the vaccine hit a major setback a year ago, when its developers announced that a miscalculation in the manufacturing process had resulted in volunteers being given lower doses than planned and that plans for the Phase 3 study would have to be delayed.

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