Policymakers are devising plans to compress the years it usually takes to develop a vaccine.

Hundreds of people are rolling up their sleeves in countries across the world to be injected with experimental vaccines that might stop COVID-19, spurring hope —maybe unrealistic — that an end to the pandemic may arrive sooner than anticipated.

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About 100 research groups are pursuing vaccines with nearly a dozen in early stages of human trials or poised to start. It’s a crowded field, but researchers say that only increases the odds that a few might overcome the many obstacles that remain.

"We’re not really in a competition against each other. We’re in a race against a pandemic virus, and we really need as many players in that race as possible,” Dr. Andrew Pollard, who is leading the University of Oxford’s vaccine study, told The Associated Press.

The first cautious tests of March the US and Europe to look for hints that different vaccine candidates really protect.

The hard truth: There’s no way to predict which — if any — vaccine will work safely, or even to name a front-runner.

As Dr Anthony Fauci, the US government’s top expert, put it: "You need more shots on goal for a chance at getting a safe and effective vaccine.”

The first cautious tests of March, when small numbers of volunteers got injections to check for side effects, have turned into larger studies in China, the US and Europe to look for hints that different vaccine candidates really protect.

Next: Finding out for sure if any of the vaccines work in the real world by testing large groups of people in areas where the virus is circulating - a tricky prospect when study participants may be in places where the virus is fading or they are told to stay home — and finding a way to quickly distribute lots of doses of any successful candidates.