In 1985, India reported around 200,000 cases of polio, the infectious disease that leaves leaves half of its survivors paralysed. In February, the country was declared polio-free ‒ no new cases have been reported since 2011.

India victory against polio is the result of a three-decade-long  Universal Immunisation Programme, which included the oral polio vaccine. A decade later, the first national polio immunisation campaign was held. "Since then, two national and multiple sub-national campaigns are rolled out every year for children up to five years of age," says Unicef.

None of this would be possible without the pioneer work of American virologist Jonas Salk, whose 100th birth anniversary is being observed today. He began his research on developing a vaccine for the disease in 1948. In 1952, he sett up the largest field trial the world had ever seen. Approximately 1.8 million US schoolchildren participated in the exercise, conducted by 20,000 doctors. But it wasn't until 1955 that the vaccine was declared to be a success. (A few years later, another US scientist, Albert Sabin, developed the version of the vaccine that is now administered to children.)

Here's a documentary about Salk made in 2009.