Phase 3 trial, recruiting 40,000 volunteers in Europe and Latin America. The company will get its first look at the data when 56 volunteers develop Covid-19. If most of them are in the placebo group, and few in the vaccinated group, it will be proof that the vaccine works.

with a lawsuit.

In April, the European Union finally fixed this shortfall, negotiating with Pfizer and BioNTech to get 1.8 billion doses of their vaccine between now and 2023. That arrangement has left analysts wondering how much demand will be left for CureVac.

“They’re going to miss the boat on the major, advanced-economy markets,” said Dr. Kirkegaard. “The U.S., Europe and Japan are going to be largely vaccinated using these Moderna and Pfizer vaccines.”

Dr. Haas countered that most of the bloc’s doses from Pfizer-BioNTech won’t come until next year. “CureVac sees itself as a major player in ending the Covid-19 pandemic in Europe and elsewhere,” he said.

Ursula von der Leyen, president of the European Commission, said that if the CureVac vaccine worked, it would be in the mix, thanks to two advantages: It is an mRNA vaccine, and it was created in Europe. It is also possible that individual European nations will make side deals with the company.

Billions of other people in low- and middle-income countries have yet to receive a vaccine, and experts say that CureVac may meet some of their demand. “We still need a lot of vaccine globally,” said Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai in New York. “I think a lot of people can benefit from it.”

The vaccines from Moderna and Pfizer-BioNTech are challenging to distribute in the developing world because of the equipment and power supply required to freeze these vaccines. CureVac’s RNA vaccine can stay stable for at least three months at 41 degrees Fahrenheit, and it can sit for 24 hours at room temperature before it is used.

“The stability is a real advantage,” Dr. Jackson said. C.E.P.I. is “in very active discussions” with CureVac, he said, about distributing the company’s vaccine through Covax, an initiative to distribute vaccines to low- and middle-income countries.

But CureVac is also designing a new generation of vaccines with a goal of eventually moving into markets in the United States and other wealthy nations. Because its potent RNA requires only a small dose, the company could potentially create vaccines for different variants and mix them in a single shot.

But such possibilities are meaningless until CureVac can prove that its vaccine works. Mary Warrell, a vaccine researcher at the University of Oxford, is reluctant to speculate about the fate of the vaccine before that milestone.

“Prediction during this pandemic has rarely been profitable,” she warned.

Matina Stevis-Gridneff contributed reporting.

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