In 1955, Canada contributed to the safe cultivation of the poliovirus, using Medium 199, and an incubation process called the “Toronto Method,” that increased quantities of the poliovirus for the trial for polio vaccine.

Medium 199 was effective for growing poliovirus in monkey kidney cell cultures without the use of animal sera37 – an important attribute as animal sera would have rendered any potential vaccine too risky for use in humans, particularly because of potential allergenic reactions to proteins in the sera. Medium 199 provided a non-allergenic base for a vaccine.

With this development, Dr. Jonas Salk of the University of Pittsburgh became confident that an inactivated polio vaccine (IPV) could stimulate the immune system enough to prevent polio in humans, just as it seemed to do in laboratory monkeys.

A breakthrough came in 1952-53, when Connaught senior researcher, Dr. Leone Farrell, developed the ‘Toronto method’ to cultivate bulk quantities of poliovirus fluids. Monkey kidney cells were first grown in Medium 199 using large ‘Povitsky’ bottles that were gently rocked in specially designed rocking machines. Technicians then carefully infected each bottle of cells with live poliovirus by means of thin glass tubes controlled by mouth. The bottles were further incubated on the rocking machines until the virus infected and destroyed all the cells, leaving a solution of poliovirus in Medium 199, which was then filtered, pooled and precisely tested for potency.

In Canada, the first news of a possible polio vaccine in the US emerged during the summer of 1953, in the middle of the country’s worst polio season. The prospect of a vaccine generated intense publicity, and raised challenging political issues for the Canadian federal and provincial governments given the substantial Canadian involvement in the vaccine’s development at Connaught.