India's Research Contributions Towards Polio Eradication (1965-2015).

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. Having learned that response to sequential doses followed arithmetic pattern and not prime-boost principle, multiple doses were tested and found to be a simple intervention to increase VE. Eventually this knowledge became critical for polio eradication. Indian research demonstrated that monovalent OPV (mOPV) had nearly three timed higher VE than trivalent OPV (tOPV). Eventually, mOPV type 1 became essential to interrupt wild type 1 infection in many locations where the VE of tOPV was very low. Indian research pointed to the epidemiologic importance of direct person-to-person spread of wild polio viruses and the need and potential of IPV to prevent and control polio. Research on vaccine responses led to the understanding that OPV would become wild-like through back mutations and to the definition of eradication as interrupting transmission of both wild and vaccine-derived polioviruses. By asking and answering the right questions insequence, Indian polio research presaged and guided polio eradication.