Events on February 23 in history

The first mass inoculation of children against polio with the Salk vaccine begins in Pittsburgh.

Jonas Edward Salk (; born Jonas Salk; October 28, 1914 June 23, 1995) was an American virologist and medical researcher who developed one of the first successful polio vaccines. He was born in New York City and attended the City College of New York and New York University School of Medicine.In 1947, Salk accepted a professorship in the School of Medicine at the University of Pittsburgh. It was there that he undertook a project to determine the number of different types of poliovirus, starting in 1948. For the next seven years, Salk devoted himself towards developing a vaccine against polio.

Salk was immediately hailed as a "miracle worker" when the vaccine's success was first made public in April 1955, and chose to not patent the vaccine or seek any profit from it in order to maximize its global distribution. The National Foundation for Infantile Paralysis and the University of Pittsburgh looked into patenting the vaccine but, since Salk's techniques were not novel, their patent attorney said "If there were any patentable novelty to be found in this phase it would lie within an extremely narrow scope and would be of doubtful value." An immediate rush to vaccinate began in both the United States and around the world. Many countries began polio immunization campaigns using Salk's vaccine, including Canada, Sweden, Denmark, Norway, West Germany, the Netherlands, Switzerland, and Belgium. By 1959, the Salk vaccine had reached about 90 countries. An attenuated live oral polio vaccine was developed by Albert Sabin, coming into commercial use in 1961. Less than 25 years after the release of Salk's vaccine, domestic transmission of polio had been eliminated in the United States.

In 1963, Salk founded the Salk Institute for Biological Studies in La Jolla, California, which is today a center for medical and scientific research. He continued to conduct research and publish books in his later years, focusing in his last years on the search for a vaccine against HIV. Salk also campaigned vigorously for mandatory vaccination throughout the rest of his life, calling the universal vaccination of children against disease a "moral commitment". Salk's personal papers are today stored in Geisel Library at the University of California, San Diego.

Poliomyelitis, commonly shortened to polio, is an infectious disease caused by the poliovirus. In about 0.5 percent of cases, it moves from the gut to affect the central nervous system, and there is muscle weakness resulting in a flaccid paralysis. This can occur over a few hours to a few days. The weakness most often involves the legs, but may less commonly involve the muscles of the head, neck, and diaphragm. Many people fully recover. In those with muscle weakness, about 2 to 5 percent of children and 15 to 30 percent of adults die. Up to 70 percent of those infected have no symptoms. Another 25 percent of people have minor symptoms such as fever and a sore throat, and up to 5 percent have headache, neck stiffness, and pains in the arms and legs. These people are usually back to normal within one or two weeks. Years after recovery, post-polio syndrome may occur, with a slow development of muscle weakness similar to that which the person had during the initial infection.Poliovirus is usually spread from person to person through infected fecal matter entering the mouth. It may also be spread by food or water containing human feces and less commonly from infected saliva. Those who are infected may spread the disease for up to six weeks even if no symptoms are present. The disease may be diagnosed by finding the virus in the feces or detecting antibodies against it in the blood. The disease occurs naturally only in humans.The disease is preventable with the polio vaccine; however, multiple doses are required for it to be effective. The US Centers for Disease Control and Prevention recommends polio vaccination boosters for travelers and those who live in countries where the disease is endemic. Once infected, there is no specific treatment. In 2018, there were 33 cases of wild polio and 104 cases of vaccine-derived polio. This is down from 350,000 wild cases in 1988. Vaccine-derived polio is a strain of the weakened poliovirus that was initially included in oral polio vaccine and that has changed over time and behaves more like the naturally occurring virus. In 2018, the wild disease was spread between people only in Afghanistan and Pakistan. In 2019, there were 175 cases of wild polio and 364 cases of vaccine-derived polio.Poliomyelitis has existed for thousands of years, with depictions of the disease in ancient art. The disease was first recognized as a distinct condition by the English physician Michael Underwood in 1789, and the virus that causes it was first identified in 1909 by the Austrian immunologist Karl Landsteiner. Major outbreaks started to occur in the late 19th century in Europe and the United States. In the 20th century, it became one of the most worrying childhood diseases in these areas. The first polio vaccine was developed in the 1950s by Jonas Salk. Soon after, Albert Sabin developed an oral vaccine, which has become the world standard.