How Long Will a Vaccine Really Take?

A vaccine would be the ultimate weapon against the coronavirus and the best route back to normal life. Officials like Dr. Anthony S. Fauci, the top infectious disease expert on the Trump administration’s coronavirus task force, estimate a vaccine could arrive in at least 12 to 18 months.

The grim truth behind this rosy forecast is that a vaccine probably won’t arrive any time soon. Clinical trials almost never succeed. We’ve never released a coronavirus vaccine for humans before. Our record for developing an entirely new vaccine is at least...