Canadian scientist Leone Farrell

Making a vaccine is not the same as mass-producing it. This Canadian scientist solved the problem for the polio vaccine — then she was largely forgotten

Leone Farrell created the standard for polio vaccine production for decades.

When American scientist Jonas Salk announced he had discovered a vaccine that could prevent polio he was hailed as a hero on front pages around the world. Parents had lived in terror of “the crippler,” which swept through Canada and the U.S. in waves during the first half of the 20th century, striking children and causing paralysis, permanent disability and death.

The promise of a vaccine even put “Polio Fighter” Salk’s face on the cover of Time magazine in 1954, and a year later the vaccine’s licensing would cement his scientific legacy. And yet Salk’s promise may have gone unfulfilled were it not for the groundbreaking work of Canadian scientist Leone Farrell toiling in obscurity at Toronto’s Connaught Laboratories.

Salk had invented a process to make a vaccine using a polio virus that he inactivated by killing it. But he had one big problem — scale. He couldn’t make enough of the virus for the millions of people who would need it or even for required field trials.