On Jun. 25, 1963, the Trivalent oral polio vaccine was licensed. The vaccine development began in 1957 by Albert Sabin to improve upon the killed Salk vaccine.

The live virus produced excellent immunity in the gut, where polio virus is primarily replicated. A living vaccine has the advantage of spreading within the community (especially where hygiene isn’t the greatest) so that it is not necessary to achieve a 100% vaccination rate.