Pioneering research has been conducted in India during the past five decades, comprehensively covering epidemiology of poliovirus infection and of polio, efficacy and effectiveness of oral and inactivated polio vaccines (OPV, IPV) as well as pathogenesis of wild and vaccine polioviruses. It was estimated, based on epidemiology data, that India had a very heavy burden of polio, with average 500-1000 cases per day. Prevention was an urgent need, but OPV showed unacceptably low vaccine efficacy (VE) for poliovirus types 1 and 3.