AAMC Reporter: August 2005

Julius Youngner (right) of the University of Pittsburgh School of Medicine, with Jonas Salk. Youngner is the only surviving scientist from the Salk team that developed the vaccine.

A World Free of Polio
50 Years After Salk's Discovery, Vaccination Still Necessary

- By Anne Blank, Special to the Reporter

One afternoon when she was 12 years old, Beatrice Sharp Slutsky was lying in the backyard of her family's home while her mother hung their laundry up to dry. Interested in acting, young Beatrice had returned home after performing in a play at a local theater earlier in the day. That afternoon, however, when her mother asked her to go inside to get more clothes pins, Beatrice suddenly discovered that she was unable to move. Her paralysis was the first indication that she had contracted paralytic poliomyelitis.

More than 50 years have passed since that afternoon, yet Sharp Slutsky, who is now 65, clearly recounts her memories of that frightening time in her life. Sharp Slutsky was one of the luckier children who contracted polio. She eventually made a full recovery from the disease, even returning to the theater and ballet, although in recent years she has developed the muscle weakness characteristic of post-polio syndrome, she said. While recovering at the D.T. Watson Home for Crippled Children near Pittsburgh, Sharp Slutsky also became one of the first 40 children to participate in Dr. Jonas Salk's groundbreaking polio-vaccine trial.

A few years later, in 1954, the trial expanded into a systematic, nationwide, voluntary collaboration, the likes of which the United States had never before witnessed. Funded solely by private donations to the National Foundation for Infantile Paralysis, now known as the March of Dimes, the trial comprised nearly 2 million children from across the country.

On a pivotal day in April 1955, the experiment culminated with the licensure of the first vaccine against polio. At the University of Michigan in Ann Arbor, Thomas Francis Jr., M.D., the director of the study, pronounced the three momentous words that have become an enduring part of this country's, if not the world's, scientific, medical, and historical lexicon. "Safe, effective, and potent" was the phrase he used to describe the vaccine for which the world had been hoping and waiting.

David Oshinsky, Ph.D., George Littlefield Professor of History, University of Texas/Austin, and author of Polio: An American Story

Hal Morgenstern, Ph.D., professor and chair of the department of epidemiology at the University of Michigan School of Public Health (UMSPH), was in the second grade at the time of the study and one of its participants. "Within a week or so after the results were announced, I think they sent out letters to the parents indicating what the results of the study were and, more specifically, whether your child had received a vaccine or not, and whether they then had to go get it," he recalled. "I had received the actual vaccine. I remember thinking that was a good thing, so I didn't have to go through it again."

Thus began a new era in the history of polio. The outstanding success of the polio vaccine led the World Health Organization (WHO) to predict that polio would be eradicated worldwide by the end of the year 2000. Indeed, the Western Hemisphere has not had a case of polio for nearly 10 years. The few cases that occurred in the 1990s were the result of the live attenuated-virus vaccine, developed by Albert Sabin, M.D., in 1961, which has an extremely small chance-about one in every 2.4 million doses, according to the Centers for Disease Control and Prevention (CDC)-of causing polio in the recipient. The last case of polio in the United States caused by the wild virus occurred in 1979, according to the CDC.

Third World Threat
In other parts of the world, however, the eradication of polio is proving to be more of a challenge. Small clusters of the disease have emerged recently in countries once thought to be free of polio, underscoring the necessity for continued vaccination of all newborns throughout the world. For example, Indonesia was thought to have eradicated the disease and had not had a case of wild poliovirus transmission since 1995, according to the WHO. In 2005, however, Indonesia reported 65 cases, with the most recent one occurring in May. Likewise, Yemen, which was once thought to be free of polio, now has 284 confirmed cases, according to the WHO.

"It's very clear that pockets of susceptibility remain in certain countries," said Arnold Monto, M.D., professor of epidemiology at (UMSPH). "Most of what we are seeing is a result of lack of immunization in those areas."

With widespread availability of a "safe, effective, and potent" vaccine, why are not all children being vaccinated? The reason, according to many experts, is that opposition to vaccination among certain groups is proving difficult to overcome.

In Nigeria, people started a boycott of polio vaccinations in 2003, after clerics in some parts of the country started rumors that the polio vaccine was a Western plot to render women infertile and to spread AIDS, said David Oshinsky, Ph.D., George Littlefield Professor of History at the University of Texas at Austin and author of the newly released book Polio: An American Story, published by Oxford University Press. Vaccinations were reinstated in July 2004, but not before poliovirus had already begun to spread.

"Not only did polio erupt again in Nigeria, but it began to leach out into neighboring countries," Oshinsky said.

In the United States, people opposed to vaccinations voice concerns over whether a type of mercury known as thimerosal, which was used as a preservative in vaccines, may cause autism. While any link between autism and vaccinations has yet to be proven, in 1999, the Food and Drug Administration recommended that drug manufacturers remove thimerosal from all products, including vaccines.

For people who remember the 1950s in the United States, polio was far more frightening than the risks associated with a vaccine. As a child during this era, Oshinsky, who also received the Salk vaccine during the nationwide trial, remembers the dreaded aspects of polio, its seemingly random attacks, and the clearly visible scars it left on its victims. These memories are what inspired him, in part, to write his book, he said.

"Polio is a very visual disease," Oshinsky said. "You see the leg braces, you see the crutches, you see pictures of iron lungs lined up in hospital wards."

While polio was never the raging epidemic it was once portrayed to be, its severity in certain susceptible individuals and the random nature of its attacks created a level of fear that surpassed even more common causes of morbidity in children, such as accidents and cancer, according to Oshinsky. In the pre-polio-vaccine era, so little was known about the disease and its epidemiology that myths about how to prevent it often spread like the virus itself.

Oshinsky remembers hearing some of these myths as a child. Because people feared that poliovirus came from the water, they were advised to prevent their children from swimming. Because people believed that the virus was transmitted in crowds, parents were told to keep their children from playing in crowded areas. Movie theaters, swimming pools, and public recreation spots were shut down during the summer, Oshinsky recalls.

"I remember my parents telling me, 'Don't play with new friends,' meaning that you had the germs of your old friends, and they didn't want you to get germs of new friends, which really were polio germs," Oshinsky said.

Achieving Eradication
Julius Youngner, Sc.D., professor emeritus of molecular genetics and biochemistry at the University of Pittsburgh School of Medicine, is the only surviving scientist from the team that developed the Salk vaccine. Youngner's work with cell cultures led to the formulation of a new technique, known as trypsinization, for growing polio that was crucial to vaccine development. Whereas previous cell cultures used to grow the virus were taken from animal neural tissue, Youngner's cultures were taken from kidney tissue, which is less likely than neural tissue to transmit contaminants. Not only was this tissue much safer to use in vaccine development, but it also made it possible for the first time to grow larger quantities of poliovirus in efforts to formulate a vaccine using the inactivated virus, Youngner said.

"We felt it was safer to kill the virus before you inoculate anybody," Youngner said. "This was a subject of great controversy at the time because the dogma was that only a live vaccine would work....Fortunately, that wasn't true."

In the United States today, children are inoculated solely with the inactivated-virus vaccine developed by Salk's team. Up until 2000, children could receive both the Salk vaccine and the Sabin live attenuated-virus vaccine. The Sabin vaccine was phased out in this country in 2000, however, because of the slight but real risk of contracting the disease.

But in developing countries, the Sabin vaccine is still used because it is easier to administer, especially where unsanitary conditions make it difficult to sterilize equipment for the injected vaccine. It is also easier to transport and is less expensive, Oshinsky explained. Once the number of polio cases drops to low enough levels-about a dozen or fewer cases per year-with the only cases occurring as a result of the live-virus vaccine, then the Salk vaccine will be used in these countries, as well, until eradication of the disease is achieved.

"The problem, of course, is that part of the reason to eradicate a virus is to be able to stop vaccinating," Monto said. "That's what we did with smallpox. And unless we do a lot better, we're not going to be able to stop."

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