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Science Flashback

The end of an epidemic

Canada's science legacy includes helping to eradicate the devastating spread of polio.

By the late 1950s, polio had been virtually eradicated in Canada. Credit: March of Dimes

By the late 1950s, polio had been virtually eradicated in Canada. Credit: March of Dimes

It's hard to imagine that a disease that once seemed pervasive and unstoppable could soon be eradicated. But that's exactly what's happening with polio, a devastating condition that was epidemic across Canada and much of the world until the early 1960s. Canada played a key role in developing and producing the first vaccine that would eventually lead to polio's eradication from most parts of the world.

Nationwide fear

Saving infant lives

Canada's legacy in vaccination research doesn't end with polio. A vaccine against infant meningitis, marketed as NeisVac-C, was developed by Dr. Harold Jennings of the NRC Institute for Biological Sciences. Meningitis causes swelling of the membranes around the brain and spinal cord. Tragically, most people who catch it are under five and one in four die within 48 hours. Survivors often have permanent brain damage or deafness. Dr. Jennings' discovery will save millions of children's lives around the world and improve the quality of life for millions of others.

The year was 1948 and fear was spreading. Canada was beginning its third and worst wave of major polio epidemics. Already thousands had died, more were paralyzed or permanently disabled, and our health-care system was stretched beyond its limits. Worldwide, many other countries were in a similar crisis, especially the U.S.

At the time, the Canadian government had introduced a Federal Health Grants Program to expand the nation's health infrastructure and support public health research, including research into the worsening polio problem. Together with Canadian life insurance companies and the U.S. National Foundation for Infantile Paralysis (also known as the March of Dimes), the program provided funding for polio research to Connaught Medical Research Laboratories at the University of Toronto, which had already established itself as a leader in vaccine science and had recently started a comprehensive polio research program. Canadians would not be disappointed with the results.

Two crucial discoveries provide hope

Dr. Leone N. Farrell of Connaught labs developed a method to mass produce poliovirus using Medium 199 in large Povitsky bottles incubated on special rocking machines. Credit: sanofi pasteur Canada Archives

Dr. Leone N. Farrell of Connaught labs developed a method to mass produce poliovirus using Medium 199 in large Povitsky bottles incubated on special rocking machines. Credit: sanofi pasteur Canada Archives

Two Canadian discoveries at Connaught were crucial to the development of what became known as the Salk inactivated polio vaccine (IPV). The first was providing the synthetic medium used to grow the poliovirus for the vaccine. Originally developed at Connaught in 1949 for cancer research and known simply as Medium 199, it contained no animal serums or proteins. This made it ideally suited as a base for the vaccine and enabled Dr. Jonas Salk in Pittsburgh to undertake the first small-scale human trials.

The second breakthrough came in 1952, and was a way to grow the poliovirus in sufficient quantities to meet the massive vaccination needs of nations. Known as the "Toronto Method," it involved gently rocking large bottles of virus culture back and forth on a custom-built rocking machine. This motion helped expose the virus to more nutrients, thereby allowing faster growth and faster production of the vaccine.

Salk vaccine, Connaught Medical Research Laboratories, University of Toronto, 1959. Credit: sanofi pasteur Canada Archives

Salk vaccine, Connaught Medical Research Laboratories, University of Toronto, 1959. Credit: sanofi pasteur Canada Archives

Using these methods, Connaught labs was able to produce 186 litres of poliovirus fluids every two weeks. This was enough for an unprecedented mass field trial of polio vaccine in the U.S. and parts of Canada in 1954.

A lasting legacy

Viruses that kill cancer

Although the poliovirus was devastating, some viruses can actually be helpful for health. For example, Dr. John Bell of the University of Ottawa has discovered several viruses that selectively invade and kill cancerous cells over normal cells. This makes them less toxic than currently available cancer therapies, which are indiscriminate. By injecting the virus into the bloodstream, Dr. Bell has effectively been able to cure cancer-infected mice. He is now working with an industry partner to develop and test the cancer-killing virus therapy in clinical trials. He's also investigating similar approaches for the treatment of HIV and hepatitis C.

Following the success of the trial, Connaught started producing the Salk vaccine for mass vaccination programs in Canada and then overseas. By the end of the decade, 44 other countries were receiving the Canadian-made vaccine. As newer research and technology became available, Canada was fast to adapt. Starting in 1959, Connaught played an important role in developing, producing and mass testing a live oral version of the vaccine that was cheaper and easier to administer.

These efforts were well rewarded. In Canada, polio epidemics peaked in 1953 with some 9,000 cases and 500 deaths, but by 1965, virtually no new cases were reported. Similar results were seen south of the border and in Europe. In 1994, Canada was declared polio free. Today, only four countries have endemic polio: Nigeria, India, Pakistan and Afghanistan. The eradication of polio is currently one of Canada's signature projects in Afghanistan.

These days, Connaught (now known as sanofi-pasteur) continues to provide the world with newer and safer polio vaccines. In 1997, the company introduced a combination product called PENTACELTM that protects against diphtheria, tetanus, whooping cough, haemophilus influenzae type b and polio. Used widely around the world, its development is entirely Canadian. End

Polio in Canada

Most Canadians under the age of 50 have never seen polio, a devastating disease that damages the motor neurons in the spinal cord and that can lead to a wide range of muscle paralyses, including life-threatening paralysis of muscles that control breathing and swallowing. The epidemic waves in Canada between 1910 and 1953 shut down schools, churches, playgrounds and other public spaces across the country. Canada was one of the hardest hit nations. During most of this period, little was known about how the disease was spread. Although most people recovered, many were left weakened, crippled or with other reminders of the disease. More than 20 million people currently live with the effects of polio, including many with post-polio syndrome, and polio survivors are one of the largest groups of disabled people worldwide.

To learn more about the history of polio in Canada:

Bernard Seytre, Mary Shaffer, The death of a disease: a history of the eradication of poliomyelitis (Rutgers University Press, 2005)

David M. Oshinsky, Polio: an American Story (Oxford University Press, 2005)

C.J. Rutty, L. Barreto, R. Van Exan, S. Gilchrist, "Conquering the Crippler: Canada and the Eradication of Polio," Canadian Journal of Public Health 96 (Mar-Apr 2005), special insert