Vaccine hunt heats up globally, still no guarantee

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.

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.