Global withdrawal of serotype-2 oral poliovirus vaccine (OPV2) took place in April 2016. This marked a milestone in global polio eradication and was a public health intervention of unprecedented scale, affecting 155 countries. Achieving high levels of serotype-2 population immunity before OPV2 withdrawal was critical to avoid subsequent outbreaks of serotype-2 vaccine-derived polioviruses (VDPV2s).

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In 1988, the World Health Assembly (WHA) passed a historic resolution to eradicate polio by the year 2000, resulting in the creation of the largest public–private partnership for health—the Global Polio Eradication Initiative (GPEI). When GPEI was launched, wild polio virus (WPV) was endemic in 125 countries and resulted annually in the paralysis of more than 350,000 people, mainly children. By 2000, the number of endemic countries had been reduced to 20, with the last WPV type 2 case occurring in 1999.

Zika virus disease is caused by a ribonucleic acid (RNA) virus, which is transmitted to humans by mosquitoes of the Aedes aegypti species. Around 80% of infections are asymptomatic. Symptomatic infections are characterized by mild fever lasting from four to seven days, associated with maculopapular rash, arthralgia, conjunctivitis, muscle pain and headache. Until recently, Zika virus disease has never been associated with deaths, intrauterine infections, or congenital anomalies. In 2013 and 2014, during an outbreak in French Polynesia, the disease was linked with GuillainBarré syndrome.

The World Health Organization declared India – among other 10 countries in South East Region – as ‘polio-free’ in 2014. Since then, the Government of India (GoI) has scaled up its initiatives against polio endgame which targets virus eradication and sequential withdrawal of type 2 virus from oral polio vaccine (OPV). However, prior to choosing the switch from trivalent OPV (t-OPV) to bivalent OPV (b-OPV), it was suggested to include inactivated poliovirus vaccine (IPV) in the national immunization schedule to protect vaccine naïve population against type 2 poliovirus.

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.