Fears of polio gripped the US in the mid-20th century. Parents were afraid to send their children to birthday parties, public swimming pools or any place where children mingled. Children in wheelchairs served as a stark reminder of the ravages of the disease. Fears of polio gripped the US in the mid-20th century. Parents were afraid to send their children to birthday parties, public swimming pools or any place where children mingled. Children in wheelchairs served as a stark reminder of the ravages of the disease. To prevent polio outbreaks, government officials used tactics now familiar in the age of COVID-19: They closed public spaces and closed restaurants, swimming pools and other gathering places. In 1952, two years before an experimental polio vaccine was introduced, there were an estimated 58,000 cases of polio and 3,145 deaths due to polio in the US. These cases included children who were left paralyzed for life. But these numbers fell dramatically after a widespread polio vaccination campaign that began in 1955. By the 1970s, there were fewer than 10 cases of paralysis due to polio in the U.S., and the polio virus was considered eradicated from the U.S. by 1979. Since then, the collective fear of the virus has mostly been lost to history—many people living today are lucky enough not to know someone who has experienced polio. Also read: New York governor declares disaster emergency after polio found in sewage So when news broke in July 2022 that an unvaccinated adult man in New York had contracted polio—the first case in the U.S. since 2013—and developed paralysis from the disease, it sent a wave of fear throughout the community. of public health and raised the question. about whether an old enemy was returning. I am a virologist and professor of immunology and microbiology and have spent my career teaching and researching how viruses can cause disease. There is no cure for polio. The only cure is prevention. And the tool for prevention is vaccination, the same tool that eliminated polio in the US in the first place. Life cycle of the polio virus Poliomyelitis – or poliomyelitis – the disease is caused by the polio virus, which is spread from person to person through the mouth. And while no one will knowingly ingest a virus, touching a contaminated object such as a spoon or glass or accidentally swallowing contaminated water can unknowingly lead to infection. When someone is infected with the polio virus, they shed the infectious virus in their stool. That’s why recent reports that the polio virus has been circulating in New York City’s sewage for months and that the virus has now been detected in three New York counties are particularly alarming. In August 2022, New York State Health Commissioner Mary Basset stated that the state health department “treats the single case of polio as just the tip of the iceberg of a much larger potential spread.” “Based on past polio cases,” he added, “New Yorkers should be aware that for every one case of paralytic polio that is seen, there may be hundreds of other people who are infected.” A single case of polio reflects a larger potential spread of the virus because most people infected either show no symptoms or have a very mild illness with flu-like symptoms. But even without symptoms, an infected person still sheds the virus in their stool, which means they can be a source of infection to others. The virus, which is very stable in the environment, is easily transmitted through surface contamination. For this reason, hand washing is a critical prevention tool. Although many disinfectants, such as alcohol or diluted Lysol, fail to inactivate the virus, chlorine bleach destroys it. This is why public health officials began chlorinating swimming pools decades ago in order to inactivate the polio virus. Typically, the human body uses stomach acid to protect against ingested viruses. But the polio virus can survive stomach acid to travel up your gastrointestinal tract. There, the virus replicates to create an infection. What is paralytic polio? Unfortunately, about one in 200 people infected with the polio virus will develop paralysis. Scientists still don’t know why one person is susceptible to the paralytic disease while most are not. In the small subset of people who get polio, the virus can attack lower motor neurons in the brainstem and spinal cord, which are important for muscle control. Infection of these neurons leads to the muscle paralysis that is characteristic of paralytic poliomyelitis. The legs are usually affected – often only on one side of the body – and the paralysis can range from mild to severe. Other muscle groups may also be affected. In the worst cases of paralytic polio, the virus can damage the centers of the nervous system that control breathing. Ventilators known as “iron lungs” were early medical devices that helped those with damaged breathing muscles, helping them breathe until their muscles healed enough to function on their own. Patients could die when the paralysis was severe and prolonged. Severity levels Although polio can be devastating to those affected by its severe form, most people’s immune systems are well equipped to fight it off. When someone recovers from polio, researchers can detect antibodies that fight the polio virus in the blood. But even long-term survivors of paralytic polio can develop late-onset muscle weakness and fatigue, which is known as post-polio syndrome. While the muscular effects of PTSD are well recognized, a number of other symptoms may be associated with PTSD, including chronic pain, sleep disturbances, cold intolerance, and difficulty swallowing. Because post-polio syndrome is diagnosed based on symptoms alone, there is no consensus on the number of polio survivors who develop it, but estimates range from 15% to over 80%. Polio prevention is key The decline in polio in the US and worldwide is a direct result of the introduction of vaccines and the public’s willingness to accept them. In 1988, the World Health Organization, in collaboration with Rotary International, the Centers for Disease Control and Prevention, and other national governments, launched the Global Polio Eradication Initiative with the goal of eliminating polio worldwide, as it has with smallpox. When this initiative began, there were still approximately 350,000 children with polio in 125 countries. In 2021, only six cases were reported. Two types of polio vaccine are used worldwide. The one used in the US since 2000 is an injection made from inactivated polio virus. Inactivation kills the virus and prevents it from spreading. Children in the US receive this vaccine at 2 months, 4 months, and between 6 and 15 months of age, and it essentially provides lifelong protection against polio. The second type of vaccine, still used in many parts of the world, is an attenuated – or attenuated – form of the virus that is taken by mouth. In places where community transmission remains important, such as Pakistan, the oral vaccine is preferred because it prevents people from contracting polio and also stops person-to-person transmission. Also read: Children under nine in London to get polio vaccine after more virus found in sewage In the US, where person-to-person transmission of the polio virus has been virtually non-existent for decades, the inactivated vaccine is preferred, as the focus is on preventing the disease in the vaccinated person and there is less concern about spreading the virus. But in extremely rare cases, the vaccine virus mutates after it is excreted in the stool. And if immunization levels fall below a critical threshold – as they do in some areas of the world – this polio virus can cause disease. The recent case of polio in New York is traced to a mutated polio virus derived from a vaccine believed to have been obtained abroad. Most people in the US are vaccinated through routine childhood immunizations. Because immunity to polio after vaccination is lifelong, the CDC does not recommend booster vaccinations for the general population for people who have completed the full series. However, the CDC recommends that anyone who has not been vaccinated against the polio virus, including adults, be vaccinated. In my office, I keep a painting of Dr. Jonas Salk, the virologist who developed the first polio vaccine. It serves as my reminder of the importance of biomedical research in eliminating human suffering caused by infectious diseases. (The conversation)
