The country has not witnessed any case of wild virus polio for three consecutive years now and that is certainly a cause for celebration.
While the first phase of the polio eradication drive using the Oral Polio Vaccine (OPV) has been successful, the nation is gearing up for the second phase using the Inactivated Polio Vaccine (IPV), said emeritus professor T Jacob John, a retired virologist from the Christian Medical College here, who is an expert on the vaccine.
Speaking to Express, Jacob said, “India was qualified by the World Health Organisation (WHO) as a polio-free country on January 13, 2014, and we have made an achievement.” He said a national commission would assess the quality of surveillance on and virological investigations into children with acute flaccid paralysis.
Once the commission certifies the country as polio-eliminated, the certification committee attached to Southeast Asia Region will declare the region free of wild virus polio, hopefully in mid-2014, he added.
The OPV is administered in the mouth and the IPV by injection. Either can be used to eliminate wild polio viruses. While all low and middle- income (LMI) countries have chosen OPV which is less expensive than IPV, other countries successfully used IPV. John said the OPV had the disadvantage of low efficacy against polio viruses types 1 and 3, especially in LMI countries, including India. “So, we had to develop monovalent and bivalent OPV to get rid of wild polio viruses.”
The OPV is genetically unstable and tend to reverse to their original nature of virulence causing ‘vaccine-associated paralytic polio (VAPP) and ‘vaccine-derived polio viruses (VDPV).’
Over 50 such cases have been reported annually. Children given OPV can shed vaccine viruses in faeces and others could also acquire secondary infection. John said, “Rooting out wild polio viruses using OPV is the first phase of the polio eradication drive that will be completed only when we make sure that no child ever gets infection. “The safe vaccine withdrawal of the live vaccine requires an umbrella of community immunity provided by inactivated vaccine and this should be the second phase of polio eradication,” he said, adding: “India is getting ready to enter this phase in 2015.”
“We need to consider the possibility of tackling the VAPP and VDPV cases already in silent circulation, if we stop giving OPV,” he said. “In the second phase, we must introduce IPV, without slowing down the tempo of OPV, to attain high coverage and sustain community immunity for a while until we know that the coast is clear of any risk of emerging or expanding transmission chains of VDPVs,” he said.