On 12 April 1955, the inactivated polio vaccine developed by Dr Jonas Salk was formally declared “safe, effective and potent”, a landmark outcome from one of the largest vaccine trials conducted to that point.

The announcement was delivered at the University of Michigan, following a nationwide field trial involving more than 1.8 million children, widely remembered as the “Polio Pioneers.”

Salk’s approach used an inactivated (killed) poliovirus, designed to stimulate an immune response without causing the disease. At the time, poliomyelitis represented a major public health threat, particularly for children, with the risk of paralysis and death during outbreaks.

The trial results demonstrated strong protection against paralytic polio, enabling a rapid transition from research to public health implementation. Vaccination programmes scaled quickly in the United States and were subsequently adopted more broadly internationally.

In the years that followed widespread immunisation:

Polio case numbers fell sharply across many settings
Large outbreaks became increasingly uncommon in countries with sustained vaccination coverage

The 1955 announcement marked a pivotal moment for vaccine science and public health planning. It also informed later advances, including the oral polio vaccine associated with Albert Sabin, which supported further progress towards global polio control.

Today, long-term vaccination initiatives led by organisations such as the World Health Organization (WHO) have eliminated polio from most parts of the world, while continued surveillance and immunisation remain important in areas where transmission persists.

Sources: history.com, cdc.gov, historyofvaccines.org, WHO.