Dozens of teams of researchers across the world are racing to develop a vaccine to stem the spread of coronavirus infections, bring down death rates, and allow countries to reopen their economies.

However, Severin Schwan, Roche’s chief executive, said he was skeptical that a vaccine could be fully tested, manufactured, and widely distributed within the next 12 to 18 months.

“I’m afraid that the most likely scenario is that we will not have a vaccine before the end of next year,” Schwan said on a Wednesday conference call with reporters, adding that an 18-month timeline is “very ambitious.”