Book summary “Polio”: summary

Introduction

You live in constant dread of a summer disease that strikes without warning, paralyzing children and leaving families helpless. You watch modern sanitation paradoxically turn a mild endemic infection into a terrifying epidemic that overwhelms hospitals and panics communities.

David M. Oshinsky chronicles the epic historical battle against poliomyelitis, detailing the scientific breakthroughs, philanthropy, and fierce rivalry that delivered the world's most famous vaccines.

You will discover how a single foundation mobilized millions of citizens to finance groundbreaking research and patient care. The book traces the path from early iron lungs to the dramatic field trials that conquered the crippling plague.

• How did modern hygiene enable the virus to strike older victims with devastating severity?
• What role did Franklin D. Roosevelt play in transforming American medical philanthropy?
• How did a bitter scientific rivalry accelerate the race for a safe and effective vaccine?

1. The Nature and History of Polio

Polio historically transitioned from a harmless endemic infant infection to a dreaded epidemic due to modern sanitation, invading the central nervous system in rare cases to destroy motor neurons.

Poliomyelitis is an enteric viral infection spread through fecal-waste contact. You will find that it primarily causes minor symptoms before clearing the body.

In about one in a hundred cases, the virus enters the bloodstream. It reaches the brain stem and central nervous system to destroy motor neurons and cause paralysis or death. Surviving nerve cells can enlarge and sprout connections to save some muscle function. Severe damage to breathing muscles leads to bulbar polio and death.

The Spread and Impact of the Disease

For centuries, poliovirus circulated freely in poor sanitary conditions. It passed harmlessly to infants and conferred lifetime immunity as an endemic disease. With twentieth-century modernization, the virus surfaced in terrifying new epidemic waves. It primarily targeted children in developed Western nations.

Early historical references to potential polio cases include an Egyptian stone tablet from around 1500 BC. This artifact shows a young man with a withered leg using a cane. Another account describes Sir Walter Scott losing the power of his right leg following a fever in the late eighteenth century.

Early American Outbreaks and Research

Dr. Charles Caverly conducted the first thorough investigation of a polio epidemic in the United States. He studied 123 cases in the Otter Valley near Rutland, Vermont, in 1894. The outbreak resulted in 50 permanent paralyses and 18 deaths.

Caverly proved that the disease could occur in epidemics and featured nonparalytic forms. He showed that the majority of victims were young males. He recognized that the traditional term infantile paralysis was misleading since older children and adults were also affected.

In 1908, Karl Landsteiner successfully isolated the poliovirus. He used spinal cord material from a dead boy in his Vienna laboratory to infect rhesus monkeys with polio.

John D. Rockefeller founded the Rockefeller Institute in New York City in 1902 to promote pure scientific research. Following the tragic death of his three-year-old grandson John Rockefeller McCormick from scarlet fever in 1900, he made medical research his primary philanthropic focus. Simon Flexner directed the institute's high-priority efforts toward conquering polio.

Flexner mistakenly concluded that poliovirus entered through the nasal passages rather than the digestive tract. By swabbing rhesus monkey nasal passages with poliovirus and observing rapid infection, he concluded that the virus traveled along nerve pathways from the nose to the spinal cord. This error misdirected polio research for decades. It caused scientists to doubt the value of blood antibody vaccines and focus instead on chemical nasal blockades.

The devastating 1916 polio epidemic in New York City triggered intense panic and discriminatory quarantines. Beginning in the immigrant neighborhood of Brooklyn known as Pigtown, the outbreak caused 8,900 reported cases and 2,400 deaths in the city. Eighty percent of deaths in New York City occurred in children under five.

During the summer of 1916, health authorities in New York City ordered the killing of 72,000 cats due to unfounded fears that they spread the paralysis. Surrounding towns deployed armed police to turn away travelers from New York with a travel certificate. Yet statistics showed that affluent, low-density areas suffered higher rates than crowded slums.

2. FDR and Warm Springs

Franklin D. Roosevelt contracted poliomyelitis at age thirty-nine, hid his disability from the public, and established a hydrotherapy center at Warm Springs, Georgia.

The Onset of Roosevelt's Illness

Franklin D. Roosevelt fell ill in August 1921 at his Campobello Island home after putting out a brush fire and participating in a strenuous cross-island race and cold swim. Following a stressful political summer, he developed fever, deep muscle aches, and progressive paralysis starting in his legs. Dr. William Keen charged 600 dollars for his initial consultation regarding the infantile paralysis.

The American antiseptic revolution of the late nineteenth and early twentieth centuries successfully eliminated many traditional diseases through hygiene. Yet it inadvertently left populations more vulnerable to severe polio outbreaks. Driven by the germ theory of disease, Americans embraced a culture of cleanliness involving pure food laws, indoor plumbing, and aggressive consumer advertising against microbes. This reduced early childhood exposure to common infections and maternal antibodies. The Lambert Pharmacal Company turned an old disinfectant into Listerine, a massive commercial success by earning 8,000,000 dollars yearly through a campaign against halitosis. Du Pont invented cellophane in 1908 during this hygiene craze.

The Creation of Warm Springs

FDR and his inner circle maintained a strict policy of concealing his severe physical disability from the public to avoid intense social stigma. Because crippled adults were frequently viewed as morally flawed or fit for institutions, Roosevelt established a gentleman's agreement with the press. He used props and long capes to project an image of a man of action before he was elected governor of New York in 1928. During political campaigns, FDR used a specially built steel bar in his touring car to stand up and locked leg braces in place.

FDR discovered hydrotherapy at a failing resort in Warm Springs, Georgia, where mineral-rich waters allowed paralyzed patients to exercise. Prompted by a letter from George Foster Peabody regarding a local man named Lewis Joseph, Roosevelt visited the property in 1924. He experienced significant buoyancy and muscle stimulation in the water, which maintained a consistent temperature of 88 degrees. In April 1926, FDR purchased the Meriwether Inn and surrounding property for 200,000 dollars to establish a rehabilitation center. John J. Raskob gave a personal check of 250,000 dollars to help FDR finance his return to politics.

Basil O'Connor and FDR formed the law firm Roosevelt and O'Connor at 120 Broadway in New York City. O'Connor was 32 when the legal partnership was formed, managing the practical side of their business. He later helped structure the Georgia Warm Springs Foundation as a nonprofit entity.

3. The March of Dimes Crusade

Franklin D. Roosevelt survived polio and became a powerful symbol of hope during the Great Depression. You watched as 1.5 million Americans were unemployed in 1929, growing to 8 million by 1931 and 30 million by 1932. Disabled individuals inundated the president with letters detailing their economic fears, social stigmas, and humiliations. Roosevelt maintained a relentlessly upbeat correspondence that provided recipients with a brief validation of their struggle.

A mother wrote to FDR saying every time she heard his voice on the radio stating handicaps don't amount to a hill of beans, her courage was renewed.

Fundraising Innovations

Carl Byoir revolutionized charity fundraising during the Great Depression by shifting the focus from large donations to small contributions. Philanthropic contributions plunged after the economic crash, forcing Byoir to organize nationwide birthday parties for FDR on January 29. The President's Birthday Ball Commission connected a popular leader with a rare disease and retained a large percentage of proceeds locally for patient care.

Contributions dropped from $369,000 in 1929 to $30,000 by 1932 before rebounding to $1,016,443 through the 1934 birthday ball committee.

On January 29, 1934, over 6,000 birthday parties were staged, culminating in a Waldorf-Astoria event where 5,000 people watched debutantes climb a giant cake while George M. Cohan performed a special ballad.

Eddie Cantor created the March of Dimes campaign to transform small coin donations into a massive national movement.

After political backlash led Byoir to resign, Basil O'Connor established the nonpartisan National Foundation for Infantile Paralysis in 1938. Comedian Eddie Cantor proposed asking citizens to mail dimes directly to the White House. The initial mail flood collected 2,680,000 dimes and established the dime as the enduring emblem of the crusade.

When Eddie Cantor launched the March of Dimes on his radio show, White House mail volume exploded from 5,000 letters a day to 30,000 on the first day, 50,000 on the second, and 150,000 on the third.

The Scientific Foundation

Premature and carelessly executed human trials of polio vaccines in 1935 resulted in paralysis and death. Maurice Brodie and William Park tested a killed-virus polio vaccine on children with minimal safety data. Simultaneously, John Kolmer tested a live-virus chemical concoction, often called a witch's brew, on over 10,000 youngsters.

John Kolmer's vaccine trials resulted in at least a dozen cases of paralytic polio, nine of them fatal, causing him to publicly wish the floor would open up and swallow him at a medical convention. Maurice Brodie died at 36 years old after these trials failed.

Thomas Rivers redirected the National Foundation's research strategy by prioritizing fundamental virology and basic science over an immediate search for a magic bullet. Appointed by O'Connor to head the Scientific Research Committee, Rivers placed the production of a vaccine at the very bottom of his priority list. He promised 300,000 dollars for a Hopkins grant over a five-year period to advance Filterable Viruses research.

You can follow Rivers's agenda through specific steps:

• identify major gaps in scientific knowledge before considering prevention and cures;
• establish university virus laboratories and public health programs where researchers work together in collaborative groups;
• allocate grants to specialists based on fundamental research priorities like pathology and viral transmission.

4. Patient Care and Treatment Innovations

Medical breakthroughs such as the iron lung and Sister Elizabeth Kenny's hot packs transformed patient care while highlighting severe societal and ethical dilemmas.

The Iron Lung and Corporate Organization

Medical engineer Philip Drinker invented the airtight iron tank in 1928 to exert push-pull motion on the chest. The respirator was originally designed to assist patients only through the acute phase until they could breathe independently. No one had considered the long-term societal and psychological implications of keeping hopelessly damaged bodies alive in these respirators over decades.

Fred Snite Jr., a wealthy young Chicagoan, contracted polio in 1936 while on a world tour and spent eighteen years living inside an iron lung before dying of heart and lung failure at age forty-three.

Basil O'Connor structured the National Foundation for Infantile Paralysis on a corporate model that centralized major decisions while relying on decentralized local chapters and volunteer fund-raising. O'Connor retained personal control over all major policy and financial decisions, while an army of salaried workers and unpaid grassroots supporters split into two groups. The first foundation chapter was established in Coshocton, Ohio, in 1939, and movie theater collections eventually grew to provide forty percent of the March of Dimes revenue by 1945.

Sister Kenny and Physical Aftercare

Sister Elizabeth Kenny revolutionized polio aftercare by rejecting immobilization casts in favor of hot wool packs and muscle reeducation to treat muscle spasms. Kenny argued that polio caused muscle spasms rather than permanent nerve damage, meaning that rigid splints and casts created deformities instead of preventing them. Her method focused on relaxing the affected areas and guiding patients to consciously reconnect their minds with paralyzed muscles through graded exercise.

Patients treated by Sister Kenny famously remembered the distinct smell and intense heat of the woolen wraps steamed in pressure cookers and applied to their limbs.

You can apply the hot pack treatment using specific technical steps:

• measure the patient's neck, shoulders, lower arms, hands, mid-section, upper and lower legs, and feet;
• cut three sets of wrappings to meet measurements using Army blankets, plastic, and cotton blanketing;
• steam the Army blanket woolen pieces in a pressure cooker until very hot;
• wrap the woolen pack piece by piece around the patient's limb and cover it with plastic;
• pin the cotton blanket on top to hold the entire assembly together;
• leave the packs on for one hour before removing them and applying a fresh set.

5. Postwar Panic and Grassroots Mobilization

The postwar baby boom and surging polio cases drove intense public anxiety, leading to the creation of the Mothers' March on Polio and sophisticated marketing strategies.

Fundraising After FDR's Death

President Roosevelt's death in 1945 stripped the National Foundation of its primary spiritual figurehead and disrupted its lucrative partnership with Hollywood movie studios. In 1946, movie studios replaced theater collections with a flat contribution, giving the March of Dimes a modest check for $30,000, which outraged foundation head Basil O'Connor.

O'Connor waged a relentless campaign against federated giving models, arguing that standalone charities were essential for maintaining public focus on unique diseases. Six-year-old Donald Anderson from Oregon, diagnosed with polio in 1943, was featured as the first official 1946 poster child showing before and after recovery photographs.

The Mothers' March and Wonder Drugs

The postwar baby boom dramatically increased the population of young children while polio cases surged, creating profound psychological panic despite low statistical mortality. In 1946, reported polio cases reached 25,000, eventually climbing to a high of 58,000 in 1952.

The Mothers' March on Polio transformed grassroots door-to-door solicitation into a highly organized, nationwide one-hour evening campaign driven by female volunteers. In Maricopa County, Arizona, on January 16, 1950, over 2,300 volunteers canvassed neighborhoods for one hour, raising $44,890 from 42,228 donors.

You can execute a successful neighborhood canvass using specific steps:

• remind people what is coming through local advertising and school flyers;
• go after local advertisers and plant slogans everywhere;
• turn on your porch light or leave a candle in the window or a shoe outside apartment doors;
• canvass assigned neighborhood blocks during the designated one-hour evening window;
• count money at the block warden level and deliver collection envelopes under police escort to headquarters.

While mid-century biomedical science successfully developed wonder drugs and antibiotics that routed bacterial infections, viral polio completely resisted these chemical cures.

6. Jonas Salk and the Killed-Virus Vaccine

In the summer of 1947, despite decades of virus discovery, epidemiologists could not explain why polio struck certain well-run environments while sparing others. Thomas Francis Jr. investigated a polio outbreak at a Pennsylvania summer camp where ten children fell ill. Despite comprehensive stool and throat swabs confirming poliovirus and thorough inspections showing clean conditions, chlorinated pools, and well-prepared food, Francis could find no solid explanation for why those few children were paralyzed while 250 others in identical surroundings remained healthy.

Jonas Salk leveraged his training under Thomas Francis at the University of Michigan to develop a killed-virus vaccine strategy at his laboratory in Pittsburgh.

The lack of scientific progress against polio drove the public to send bizarre theories and dangerous proposed cures to researchers. Frustrated by the mystery of polio, ordinary people flooded scientists like Albert Sabin and Peter Olitsky with letters attributing the disease to rotten fruit, horse manure, ripe corn, bird droppings, mold on cake, beetles, and groundhogs. Proposed cures included canine feces and injecting patients with their own urine.

A German doctor wrote to Peter Olitsky suggesting that polio patients be injected with their own urine, noting side effects such as infection, joint pain, mental depression, sore throat, and fever.

Basil O'Connor appointed Harry Weaver as director of research at the National Foundation to streamline the agenda and shift focus toward a vaccine. Faced with widespread frustration and a lack of coordinated progress among grantees who viewed research primarily through the lens of academic curiosity, Weaver pushed for group planning and pooled ideas, concluding that a vaccine was the only viable solution because the virus could not be purged from the environment or blocked by drugs.

The Scientific Guessing Game

City College of New York served as an intense, tuition-free meritocracy that launched the careers of many working-class immigrant intellectuals, including Jonas Salk. Entering college at age fifteen, Salk navigated an intensely competitive academic environment populated largely by ambitious Jewish students from immigrant families. By 1930, 80 percent or more of the student body comprised Jews, and eight Nobel Prize winners emerged from the ranks of City College students of the 1930s and 1940s. Jonas Salk entered the City College of New York as a freshman a month before his sixteenth birthday.

NYU College of Medicine provided Salk with an encouraging environment free from the rigid Jewish quotas enforced by many other medical schools at the time. While surrounding elite institutions like Yale, Cornell, and Columbia maintained strict quotas limiting Jewish admissions, NYU welcomed qualified applicants. In 1935, Yale accepted only five Jewish applicants out of roughly 200 who applied, operating under explicit quotas. Salk excelled in laboratory work and clinical applications, eventually securing an elite internship at Mount Sinai.

The catastrophic death toll of the 1918 Spanish flu shaped military priorities and drove wartime investments into influenza vaccine research. The 1918 influenza pandemic infected half the world's population, killed one in twenty, and disproportionately targeted young adults in close quarters. Remembering these losses, military leaders during World War II heavily funded Thomas Francis to develop a safe and effective vaccine for troops. 1 American in four took sick and at least a half million died during the 1918 pandemic, and the Spanish flu killed 44,000 American military personnel, a number nearly matching the 50,000 battle deaths.

Salk's Apprenticeship and Move to Pittsburgh

Thomas Francis and Jonas Salk championed a killed-virus vaccine approach over the live-attenuated tradition to ensure safety without risking infection. Most virologists believed lasting immunity required a low-grade natural infection using a live-attenuated virus. Francis argued that a properly inactivated killed-virus vaccine could safely trick the immune system into producing protective antibodies without the danger of reverting to virulence. Thomas Francis experimented with ultraviolet light and formaldehyde solutions at the University of Michigan to fully inactivate influenza viruses without destroying their immunizing properties.

During his six-year apprenticeship under Thomas Francis at the University of Michigan, Salk mastered laboratory techniques, vaccine preparation, and mass-testing methods. Working under Army grants and National Foundation support, Salk helped develop and test influenza vaccines on soldiers, mastering formalin inactivation and strain collection. 4,700 dollars was Salk's initial annual salary as a research associate at Michigan, which rose to 6,000 dollars annually after his 1946 promotion. In the fall of 1943, Salk and Francis tested an influenza vaccine on several thousand soldiers, demonstrating that killed virus strains produced a strong antibody response.

In 1947, Salk accepted a position heading a new virus research program at the University of Pittsburgh to secure complete professional independence. Despite colleagues warning him that Pittsburgh was a stagnant research backwater, Salk seized the opportunity to build his own laboratory. Backed by Dean William McEllroy's vision and 30,000 dollars in seed money provided to Pittsburgh's medical school in 1946 by the National Foundation, Salk established his operations in a hospital basement and strategically positioned himself to research both influenza and polio. Jonas Salk accepted the directorship of a new virus research program at the University of Pittsburgh in 1947, setting up his initial lab in two bare rooms in the basement of Municipal Hospital.

7. The Pathway to a Vaccine

Groundbreaking laboratory projects identified the three poliovirus types, perfected monkey kidney tissue culture, and established the bloodstream route of infection.

Harry Weaver revolutionized medical research funding by introducing overhead cost coverage and strict milestone accountability. He addressed university complaints about overhead by creating a sliding scale to cover indirect costs and insisted on reviewing annual progress to terminate lagging grants and redirect funds.

• If the grant is $10,000 or less, increase the amount by 46%.
• If the grant is between $10,001 and $30,000, increase the amount by 46% for the first $10,000, and 38% of all remaining.
• If the grant is more than $30,000, increase the amount by 46% of the first $10,000, 38% of the next $20,000, and 6% of all remaining.

Jonas Salk utilized foundation grants and indirect cost reimbursements to rapidly expand his laboratory operations in Pittsburgh. Salk capitalized on unused space in Municipal Hospital, scaling up his staff and facilities to handle massive virus-typing and vaccine development workloads. Between 1949 and 1953, he received almost $1,000,000 in total grants from the National Foundation, alongside $255,000 in additional money going to indirect costs.

Typing the Poliovirus and Experimental Logistics

A massive foundation-backed typing project proved that all known poliovirus strains fit into three distinct types. Researchers tested 196 strains to map this manageable family, spending $1,200,000 to identify 82 percent in Type I, 10 percent in Type II, and 8 percent in Type III.

• Inject fecal samples from human polio victims into the brains of monkeys.
• Exercise the animals daily to look for telltale signs of polio.
• Destroy paralyzed animals to harvest their brains and spinal cords for poliovirus.
• Inject tissue-serum mixtures of the virus into the brains of healthy monkeys to test for immunity against specific types.

David Bodian, Jonas Salk, and other researchers named the discovered categories Brunhilde, Lansing, and Leon. The mass collection and processing of monkeys were vital logistical components of early polio research. The National Foundation established Okatie Farms in South Carolina in 1949 to screen, feed, and condition rhesus and cynomolgus monkeys imported from India before distributing them to researchers.

Dismantling Dogma and Tissue Culture

John Enders discovered that poliovirus could be grown in non-nervous tissue culture, enabling safe mass production. He received a $200,000 research grant from the National Foundation and challenged Simon Flexner's dogma that poliovirus could only grow in neural tissue by successfully cultivating viruses in embryonic skin, muscle, and kidney tissues.

Working at the Children's Hospital of Boston, Fred Robbins and Tom Weller inoculated tissue cultures containing non-nerve embryonic tissue with poliovirus under Enders's guidance.

Experiments discredited Simon Flexner's theories on the nasal pathway and chemical blockades, redirecting focus to the alimentary canal. Failed attempts at chemical blockades, such as spraying zinc sulfate which caused a permanent loss of smell, forced researchers to reinvestigate how polio entered the human body. Albert Sabin used autopsy material to prove the olfactory pathway was not involved, and Howard Howe and David Bodian severed chimpanzees' olfactory nerves and still infected them by mouth.

Researchers proved that poliovirus passes through the bloodstream during incubation before reaching the central nervous system. Dorothy Horstmann and David Bodian demonstrated that poliovirus is present in the blood only during a brief incubation window before neutralizing antibodies are formed. Horstmann fed poliovirus to chimpanzees by mouth and successfully detected the virus in their blood within days.

8. The 1954 Field Trials and the Ann Arbor Triumph

The National Foundation executed the largest public health experiment in history, culminating in the triumphant Ann Arbor announcement that Salk's vaccine was safe and effective.

The Scale of the Field Trials

You watched the National Foundation for Infantile Paralysis launch the 1954 Salk vaccine field trials. This managerial mobilization aimed to vaccinate approximately 650,000 schoolchildren without any federal assistance or prior precedent. Melvin Glasser coordinated a vast network of volunteers and medical personnel to manage the complex operations.

Recruitment reached massive proportions across the country:

• 14,000 school principals needed;
• 50,000 classroom teachers needed;
• 20,000 physicians needed;
• 40,000 nurses needed;
• 200,000 to 250,000 non-professional volunteers needed.

Basil O'Connor rejected federal funding to avoid bureaucratic red tape and ideological conflict. The January 1954 March of Dimes campaign raised $55 million, followed by an August warm-weather appeal that brought in $20 million. In 1953, the foundation spent about $2 million on polio research compared to less than $75,000 spent by the National Institutes of Health.

Planners whittled the final selection down to 211 counties across 44 states to involve nearly 1.5 million schoolchildren in the experiment. You can see how researchers structured the project using strict criteria:

• Select second-grade children to receive the vaccination procedure because comparable pre-vaccination records are available for adjacent grades.
• Compare post-vaccination experience with concurrent experience in non-vaccinated children in the first grade and third grade.
• Use second-grade children because they are better adjusted psychologically to school life and offer less resistance to a three-dose procedure.

The Ann Arbor Announcement and Aftermath

Thomas Francis directed an independent and scientific evaluation at the University of Michigan using a blank-check budget. Francis employed 120 people, including graduate students, Census Bureau statisticians, and IBM punch-card drum memory machines to process records for 1,349,135 children. Graduate students received $1.25 an hour for editing and coding data under strict privacy conditions.

On April 12, 1955, Francis delivered his 98-minute evaluation report at Rackham Hall in Ann Arbor. Dave Garroway announced on NBC's Today show that the vaccine was safe, effective, and potent while schoolchildren cheered and church bells chimed.

The results demonstrated clear statistical success:

• 80–90 percent effectiveness against paralytic poliomyelitis in injected study areas;
• 60–70 percent effectiveness against Type I virus;
• 90 percent or more effectiveness against Type II and Type III virus.

Jonas Salk famously refused to patent the vaccine when Edward R. Murrow asked about ownership on television. Salk declared that the work belonged to the people and asked if one could patent the sun. Patent attorneys had already confirmed that his use of tissue culture and formalin contained no significant novel inventions.

10 Key Ideas

1. Modern sanitation paradoxically transformed poliovirus from a harmless endemic infant infection into a terrifying epidemic wave of paralysis and death.
2. Stricken at age thirty-nine, Franklin D. Roosevelt concealed his disability and established a rehabilitation hydrotherapy center at Warm Springs, Georgia.
3. Eddie Cantor and Basil O'Connor transformed small coin contributions into a massive national movement through the March of Dimes campaign.
4. Medical engineer Philip Drinker invented the iron tank respirator to assist patients through the acute phase of respiratory paralysis.
5. Sister Elizabeth Kenny revolutionized polio aftercare by replacing immobilization casts with hot wool packs and muscle reeducation.
6. The postwar baby boom and surging polio cases drove intense public anxiety, leading to the creation of the Mothers' March on Polio.
7. Jonas Salk leveraged his training under Thomas Francis at the University of Michigan to develop a killed-virus vaccine strategy at his laboratory in Pittsburgh.
8. John Enders discovered that poliovirus could be grown in non-nervous tissue culture, enabling safe mass production and disproving Simon Flexner's neural dogma.
9. The National Foundation executed the largest public health experiment in history by vaccinating hundreds of thousands of schoolchildren across the country.
10. Thomas Francis delivered the triumphant Ann Arbor announcement confirming that Jonas Salk's vaccine was safe, effective, and potent.