📅 12 April 1955
Investigators reported that the inactivated vaccine had protected participants in a large trial.
📅 12 April 1955
US authorities licensed the vaccine on the day the trial results were presented.
📅 12 April 1955
The announcement opened a new phase of polio immunization, requiring manufacturing and access.
📅 12 April 1955
The findings followed participation by many families, healthcare workers and researchers.
