Two doses of a new Covid vaccine that is based on a conventional approach achieved 100 per cent efficacy against severe disease and hospitalisations, and it could be an effective booster after other Covid shots, the vaccine’s manufacturers announced on Wednesday.

The vaccine, made by the Europe-based pharmaceutical companies Sanofi and GSK, is one of four candidates that received billions of dollars for development from Operation Warp Speed, the Trump administration’s programme to accelerate vaccines.

The new vaccine had an efficacy of 75 per cent against moderate-to-severe disease. It showed 58 per cent efficacy against symptomatic disease in its Phase 3 clinical trial. Although that number is lower than was observed for the mRNA vaccines made by Pfizer-BioNTech and Moderna in their initial trials, it is “in line with expected vaccine effectiveness in today’s environment dominated by variants of concern”, Sanofi and GSK said in a statement.

Used as a booster dose after one of the other available coronavirus vaccines, the Sanofi-GSK shot increased antibody levels by 18- to 30-fold. The companies intend to submit the vaccine for authorisation to regulatory authorities in the US and Europe, they said on Wednesday.

Sanofi and GSK were expected to seek authorisation for their vaccine last year, but shelved those plans after clinical trials showed disappointing results in older adults. They then developed a stronger version of the vaccine and tested it in new trials.

In laboratory studies, two doses of the Sanofi-GSK vaccine delivered more neutralising antibodies than an approved mRNA vaccine, according to the companies. The data have not yet been published. The vaccine was safe and well-tolerated by adults of all ages, the companies said.

The best target for Covid vaccines is a protein called spike that covers the surface of the virus like a crown. While the mRNA vaccines contain the genetic instructions for making the protein, the Sanofi-GSK vaccine uses a slightly modified version of the protein itself to stimulate an immune response.

This is a commonly used approach for vaccines, and so may convince some people who have been hesitant to adopt the newer mRNA technology. Protein-based vaccines are also relatively inexpensive to manufacture and may not require the ultracold storage needed for the mRNA vaccines.

New York Times News Service