NPR has a great piece this month commemorating the 60th anniversary of the Salk vaccine for polio. Few episodes are as deeply encoded in the national memory as the polio outbreak of the 1950s. Those old enough to remember the debilitating disease recall the widespread fear it wrought and its devitalizing effect on the postwar American psyche. My parents have told of going to school in central Virginia and seeing classmates navigating the halls on crutches and wheelchairs, of unperturbed swimming pools and deserted theaters, and of rubber-limbed paralytics vegetating away in iron lungs. For them, these images are indelible, but they also recall how this story ended—with a pair of vaccines that brought a grim-faced generation back from the brink.
While polio is an ancient disease, it didn’t ignite European and American fears until the turn of the 20th century, when scattered epidemics began surfacing in urban centers and schools. By the early 1950s, polio had become the worst outbreak in America’s history. Children under the age of 5 were most susceptible to the virus, and 1 in 200 infected would progress to paralytic polio. 5 to 10% of these would succumb to the illness within a year.
Salk and colleagues began their in vitro testing using HeLa cells in 1952. Similar to the seasonal flu vaccine developed by the CDC, Salk employed a “trivalent” approach using inactivated DNA from three different virus strains. Such an approach offers cross-protection from sister strains, even if the vaccine isn’t a perfect match for an individual strain. (There are a number of ways to make an antibody to ‘X’.) In three years’ time, Salk’s remedy was licensed for use and exported to medical facilities around the world.
Prestige and history books tend to favor first to market producers, but Salk’s race to eradicate polio was far from a solo venture. Other major players included Hilary Koprowski, Herald Cox and Albert Sabin. The latter trio represented the dominant view of virology at the time. Harkening back to the principles laid down by Edward Jenner and Louis Pasteur, they contended that all vaccination efforts should be predicated on attenuated (weakened) versions of the pathogen. Dead versions injected into the bloodstream, a la Salk, would not produce a strong enough immune protection for long-lasting prevention, they argued. Bitter rivalries broke out among all parties.
While the Salkian view was decidedly in the minority, his research was progressing much more quickly than the competition and, perhaps just as importantly, he had the support of his mentor, Dr. Thomas Francis, Jr. at the University of Michigan, one of the most renowned virologists in the field. Francis oversaw the national field trial, and when he announced the results on April 12th of 1955, the next-morning’s headlines captured the spirit of the era. The New York Times edition read: “Salk Polio Vaccine Proves Success – Millions Will Be Immunized Soon”.
Salk’s IPV (inactivated poliovirus vaccine) may have been a resounding and immediate success, but all work on polio prevention did not halt when his product went out the door. Koprowski, Cox and Sabin trotted the globe conducting field trials and jockeying for licensure of their preferred remedy. In his book, Polio: An American Story, David Oshinsky recounts the major hurdles before them. The efficacy of the Salk booster having already been demonstrated, many people wondered why another vaccine was needed. There were also lingering fears that active forms of the virus could trigger the very disease vaccination was meant to prevent.
The latter concern was not unfounded. Just four weeks after the Salk IPV received the green light, the Surgeon General placed a nationwide ban on polio vaccine manufacturing and an embargo on exports after new cases appeared in children given the vaccines. IPVs originating from a single facility in Berkeley were found to contain live virus material; the inactivation process had failed, and lab protocols hadn’t caught it. The oversight resulted in some 200 new cases of polio, including 11 deaths. The consensus of virologists converged on a different, less virulent strain for one of the three used in the IPV, and since the incident in 1955 no vaccine-associated cases have been recorded by the CDC.
Research on alternative techniques surged ahead, including Albert Sabin’s oral vaccine, prompting the National Institutes of Health to set up a special committee in 1958 to assess the relative merits of inactivated versus attenuated immunization and oral versus intravenous transmission. Sabin had procured two strains: one based on a single viral type and another based on a mixture of all three. Over the next three years, his prototypes were used to vaccinate more than 115 million children throughout the Soviet Union, Eastern Europe and Singapore. Due to its superior success abroad, Sabin’s trivalent vaccine won out and quickly became integral to global eradication efforts. Today, most countries use Sabin’s OPV (oral poliovirus vaccine) for reasons relating to cost, ease of use and longer-lasting protection.
Plagues like polio have brought civilizations to their knees throughout recorded history. But thanks to the work of enterprising scientists like Salk and Sabin, and organizations like the Global Polio Eradication Initiative and its partners, we are fighting back. Today polio is near to following in the footsteps of smallpox. The virus has all but vanished save for three countries—Nigeria, Pakistan and Afghanistan—compared with 125 countries in 1988 when GPEI began. NPR speaks to the impact Salk’s original vaccine had on the American mood in the spring of 1955:
And yet even now, there are parents as informed about science as fish are of land refusing their kids the benefits of vaccination and their local communities the herd immunity it confers. All because of spurious claims by plastic media pundits and that thing that was said by Neighbor Joe that one time at a bbq last fall. Shame on Neighbor Joe for his uninformed banter, and shame on parents for taking Neighbor Joe even semi-seriously. Many baby boomers are alive today because they didn’t die from polio. We all would like our children to say the same about equally pernicious, equally preventable diseases in a generation. Stand up for established science and against illiterate, stark-gibbering mad dogmatism. There’s a lot of both.
External Link: Defeating Polio, The Disease That Paralyzed America
— Polio: An American Story by David Oshinsky
— Splendid Solution: Jonas Salk and the Conquest of Polio by Jeffrey Kluger