In 1954, the first vaccine against polio, developed by US scientist Dr. Jonas Salk, is ready for mass testing. Called inactivated polio vaccine (IPV) and based on a killed virus strain, its introduction creates a sensation in countries panicked by epidemics. In 1957, US researcher Dr. Albert Sabin, shown here, introduces the oral polio vaccine (OPV), derived from a weakened live virus. By the mid-1960s, OPV would largely replace Salk's vaccine because it provided complete 'gut' immunity, was easier to administer and cost less to manufacture. In 1988, it would become the vaccine of choice for global eradication.