Which vaccine did Jonas Salk announce as safe and effective in 1955?

Jonas Salk announced that his inactivated polio vaccine was safe and effective in 1955.

Salk led a research team at the University of Pittsburgh that developed a vaccine using killed poliovirus. Because the virus was inactivated, it could not reproduce, while still presenting viral material to the immune system. Large field trials involving more than 1.8 million children in the United States, Canada, and Finland produced the evidence behind the announcement.

On 12 April 1955, the results were publicly announced at the University of Michigan. The news came during a period when polio epidemics regularly frightened families and could cause paralysis or death, particularly in children.

Albert Sabin later developed an oral polio vaccine using weakened live virus. The two vaccines have different properties and have both played major roles in reducing polio. Salk is therefore associated with the injected inactivated vaccine, not with the later oral vaccine.