Fair enough. I was solely relying on the literal context of the quoted passage from Breakthrough, “...On April 12, 1955, the world learned that a vaccine developed by Jonas Edward Salk, M.D., could be relied upon to prevent paralytic poliomyelitis.” Thanks for the response.

Information travels quickly. “Surprises“ tend to be few and far between or anticlimactic. 

The world didn’t learn that there was a vaccine that could reduce likelihood of COVID infection in the same manner described above regarding polio. The world was incrementally exposed to daily/hourly progress reports of the vaccine development. 

When approved under EUA policies, it was just the next logical and incremental step in a protracted series of events.