When Jonas Salk's polio vaccine was found to be safe and effective in 1955, following a successful trial involving nearly two million American children, it marked a turning point in the fight against a highly infectious disease causing incurable paralysis or even death. Prior to Salk's discovery, between 25,000 and 50,000 cases were recorded each year in the United States alone, and little was known about how the virus spread.
Salk created his injectable inactivated polio vaccine (IPV) by treating the virus with formalin. Around the same time, Albert Sabin was developing an oral polio vaccine (OPV), which uses attenuated (weakened) mutant strains that stimulate antibody production without causing the disease. Cheaper and easier to administer than IPV, Sabin's live-virus version ultimately became more widespread in the global effort to eradicate polio, although it was introduced six years later.
