British pharmaceutical company GlaxoSmithKline (GSK) and its French partner Sanofi are seeking regulatory approval for their COVID-19 vaccine in the US and Europe, the companies announced on Wednesday. 

The companies will be submitting data from their Phase 3 trials for their two-dose regimen with shots spaced three weeks apart. These doses demonstrate 58 percent efficacy against any signs of symptomatic COVID-19, they report, and 100 percent efficacy against severe COVID-19 disease and hospitalizations. The companies will also be submitting data from their booster trials, to show how their shot can increase immunity in individuals regardless of their initial vaccine types. GSK and Sanofi said in a statement that full results for both studies will be published “later this year.”

Unlike the COVID-19 vaccines already on the US market, GSK and Sanofi’s vaccine is protein-based. The formulation contains benign material from the surface of the SARS-CoV-2 virus, which triggers a protective immune response in recipients when the body’s immune cells come into contact with it. It’s an older, more traditional type of vaccine than mRNA, which Pfizer and Moderna use, or adenovirus vector vaccines, like the Johnson & Johnson shot. It can also be stored at common refrigerator temperatures, not requiring the ultracold storage that other vaccines do.  

“In the developing world, where there are still large unvaccinated populations, the ability to store protein based vaccines at normal refrigerator temperatures could facilitate distribution,” Jefferies analyst Peter Welford wrote to Barron’s.

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Other companies around the world are either offering or developing their own protein-based COVID-19 vaccine. Novavax has begun shipping its vaccine across the European Union. China’s Clover Biopharmaceuticals has signed a long-term agreement to supply UNICEF with its vaccine as part of the COVAX initiative.

It may seem as though these protein-based vaccines are late to the game, with so many people already fully vaccinated, especially in Western countries. But Nick Jackson, head of programs and innovative technologies at the Coalition for Epidemic Preparedness Innovations, told Nature that “protein vaccines are going to beckon in a new era of COVID-19 immunization.” He added, “the world needs these protein-based vaccines to reach those vulnerable populations.”

GSK and Sanofi expected their vaccine to be ready much earlier. Nature reported that in early trials, faulty reagents resulted in dosing miscalculations, causing early participants to receive doses that were approximately one-fifth the planned amount. The mistake set their development timeline back months.

Now, GSK and Sanofi finally have their vaccine trial efficacy numbers. Efficacy against symptomatic disease is a little low compared to other trials—those for the mRNA vaccines, for example. But “no other global Phase 3 efficacy study has been undertaken during this period with so many variants of concern, including Omicron,” Executive Vice President of Sanofi Vaccines, Thomas Triomphe said in a statement.  All in all, he said, “we’re very pleased with these data.”