Polio Elimination Due to Vaccination, Not End of Pesticide Use

SciCheck Digest

Polio, a paralytic disease caused by a virus, has been eliminated in the U.S. — and nearly wiped out globally — thanks to vaccines. But social media posts are reviving old, false claims that polio is instead caused by pesticides and outbreaks of the disease ended when people stopped using DDT.

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In the 1940s and 1950s, Americans were terrorized by the threat of polio. Every summer, the highly contagious viral disease caused outbreaks that killed or paralyzed people, most of them children. At polio’s peak in 1952, there were nearly 58,000 cases in the U.S., including more than 3,000 deaths and 21,000 instances of mild or disabling paralysis.

Relief came with the development of polio vaccines: first, with Jonas Salk’s vaccine, made from inactivated, or killed, polioviruses, in 1955, followed by Albert Sabin’s oral vaccine, made from weakened polioviruses, in the early 1960s.

With widespread vaccination, polio cases quickly plummeted. In 1960, 2,525 paralytic cases were reported in the U.S. — a decline of nearly 90% from 1952 — and there were just 61 cases in 1965, according to the Centers for Disease Control and Prevention. Wild poliovirus was eliminated in the U.S. in 1979, meaning there is no ongoing transmission of the virus. Vaccination efforts across the globe have since come close to eradicating the virus. As of last year, wild poliovirus was circulating in just two countries — Pakistan and Afghanistan — according to the World Health Organization.

Despite this well-documented history, posts on social media are circulating false claims that polio is caused by pesticides such as DDT — and that outbreaks subsided not because of vaccination, but because people stopped spraying the chemicals.

“Polio stopped when they stopped dousing the population [with] DDT not some injection,” a popular Instagram post falsely reads.

“Polio wasnt some single strain virus eradicated by a miracle vaxx,” the post’s caption continues. “It was pesticides like Lead Arsenate and its more lethal replacement DDT that lead to lower spine lesions through the gut.”

The Instagram post, which includes three images of DDT being applied on or near people, garnered more than 15,000 likes in its first day. It was subsequently shared on Facebook.

A YouTube video making the same claim — but going further to incorrectly suggest that viruses, including SARS-CoV-2, which causes COVID-19, don’t cause disease and don’t even exist — was also recently shared online.

A child with polio learning to walk at Queen Mary’s Hospital, London, in 1947. Photo by George Konig/Keystone Features/Getty Images.

These claims are false. There is no doubt that polio is caused by a virus. This discovery was made in 1908, when scientists injected two monkeys with filtered spinal cord fluid from a boy who had died of polio. The monkeys developed polio and died. Because of the filtration steps, the scientists concluded polio was caused by something smaller than bacteria, likely a virus. Subsequent studies confirmed this. In the 1950s, the virus was observed under an electron microscope.

The polio vaccines themselves are also a testament to the viral nature of polio, since they are made of weakened or killed polioviruses. The scientists who figured out how to isolate and grow poliovirus in a variety of cell types, thereby enabling vaccines, won the 1954 Nobel Prize in physiology or medicine.

There is no evidence that pesticides such as DDT cause polio, or that discontinuing certain pesticides “ended” polio. 

For one, polio existed well before DDT. DDT, or dichloro-diphenyl-trichloroethane, wasn’t synthesized until 1874, but polio likely goes back at least several millennia to ancient Egypt.

Nor does the removal of DDT line up with polio’s descent, as our colleagues at Health Feedback noted when addressing similar claims in 2020.

“The peak year for use in the United States was 1959 when nearly 80 million pounds were applied,” the Environmental Protection Agency wrote of DDT in a 1972 press release announcing a ban on agricultural use of the chemical. “From that high point, usage declined steadily to about 13 million pounds in 1971, most of it applied to cotton.”

In 1959, polio had already begun its massive decline with the rollout of Salk’s vaccine. Even ignoring issues of biological plausibility, the timelines don’t match up.

Polio cases, as we said and have explained before, dropped only with the advent of vaccination.

The only connection we could find between DDT and polio is that in the 1940s and 1950s, some U.S. communities sprayed DDT in a misguided effort to avert polio outbreaks, as University of California Berkeley historian Elena Conis has documented. 

A 1971 transmission electron microscopic (TEM) image shows numerous poliovirus type-1 virions. CDC/Dr. Joseph J. Esposito; F. A. Murphy.

At the time, it wasn’t known how polio spread — through contact with feces, and to a lesser extent sneezes or coughs — and some suspected flies could be the culprit. DDT had proven to be immensely successful during World War II in fighting insect-borne diseases such as typhus, malaria, dengue and yellow fever. But of course, it would take vaccines to finally quell polio outbreaks.

It’s important to note that while polio is no longer the scourge it once was, the disease remains a risk to Americans who are unvaccinated because cases can be imported. In the U.S., children receive four doses of the inactivated polio vaccine, which are more than 99% effective in preventing severe polio.

Because other countries still use the oral vaccine, which contains weakened but live virus, it’s possible in rare cases for unvaccinated people in the U.S. to develop polio from vaccine-derived strains of poliovirus that originate from people vaccinated abroad and circulate in the community. This appears to be what happened this past summer in an unvaccinated man in New York, as we’ve written.

Fortunately, vaccination protects against polio from wild and vaccine-derived strains, which is why health officials have encouraged anyone who has skipped their polio vaccines to get caught up.