In 1952, Dr. Jonas Salk and his team found monkey kidney tissue to be the most fertile environment for virus growth and were able to grow the virus at unprecedented levels, thanks to Dr. Julius S. Youngnerﾒs development of trypsinization, the standard approach still used in labs worldwide today.

The team also refined their methods to reliably kill the virus with formalin while preserving its ability to induce protective antibodies. Monkeys injected with this vaccine showed no ill effects and developed high levels of protective antibody within 21 days. After only one year of trials, animal immunizations had proven successful.