After nearly five polio-free years, and with the launch of the inactivated polio vaccine (IPV) injection in the national immunisation programme tomorrow (November 30), India will be pushing for “endgame polio”.
The injectable vaccine, which uses killed polio viruses, will be used alongside the oral polio vaccine (OPV).
For now, immunisation using IPV will be restricted to Bihar, Chhattisgarh, Gujarat, Madhya Pradesh, Uttar Pradesh and West Bengal. In the first quarter of 2016, it will be expanded to the other Northern and Northeastern States and in the second quarter, will encompass the four southern States and Maharashtra. “Immunisation using IPV injection is in a reverse order, with the well performing States getting it last,” said virologist Dr. Jacob John, formerly with the Christian Medical College, Vellore.
Though cheap and easy to administer, OPV HAS an inherent safety issue —in rare cases, live viruses used in a weakened form can turn virulent, spread within communities and cause polio in unprotected children. In 2011, such a scenario caused seven vaccine-derived poliovirus (VDPV) cases in India.
IPV aims to prevent vaccine caused polio cases, where viruses used in OPV cause flaccid paralysis. Till date, India, like many other countries, has been relying on an OPV campaign-style programme several times a year to keep the naturally-occurring wild polioviruses at bay.
All three strains of the poliovirus (type 1, type 2 and type 3) are used in OPV. Of these, type 2 is responsible for more than 95 per cent of VDPV cases. Ironically, type 2 wild poliovirus had been eradicated since 1999. Since then, all type 2 cases have been caused solely by vaccine polioviruses.
The move also marks a shift in addressing vaccine-derived poliovirus cases, with the Global Polio Eradication Initiative removing the type 2 strain globally from OPVs.
To begin with, one dose of IPV will be administered along with the third dose of OPV and DPT to children who are 14 weeks old. Even after being immunised with IPV, it is essential that all children are immunised with OPV every time it is offered. IPV when used in combination with OPV can quickly boost immunity against poliovirus and offer double protection.
“One dose of IPV will prime the immune system and the immune response will be quicker whenever OPV or IPV is given subsequently”, said Dr. Pankaj Bhatnagar, Technical Officer of the WHO India National Polio Surveillance Project, New Delhi.
There is a scientific reason for choosing 14 weeks for IPV immunisation. “When IPV is given to children at 14 weeks and later, nearly 70 per cent of them will develop antibodies against polio viruses. It will be around 30 per cent if given to children younger than 14 weeks”, he said.
The switch from OPV with all three strains to only two strains (type 1 and type 3) will happen towards the end of April 2016. “India will make a switch from a trivalent [containing all three virus strains] to a bivalent [containing only two strains] on April 24,” Dr. John said.
“There are a risk when this switch is made,” he warned. “Vaccine-derived type 2 will spread silently and cannot be stopped and children will continue to shed type 2 strain for 4-6 weeks after the last OPV dose. [A] new crop of children who do not get the trivalent oral polio vaccine can get exposed to [the] type 2 strain shed by vaccinated children,” he said.
It is to minimise this that the Global Polio Eradication Initiative requires all countries using the three-strain to introduce at least one dose of the injectable vaccine before making the switch.
“We will be building the immunity of the community against type 2 through IPV and OPV immunisation so that at the time of switching from trivalent to bivalent OPV there will be no risk,” said Dr. Pradeep Haldar, Deputy Commissioner – Immunisation, Ministry of Health and Family Welfare, Government of India.
Since the injectable vaccine contains all three strains in a killed form, it cannot cause vaccine-derived poliovirus. Superior safety apart, IPV has other advantages. Nearly 60 per cent who receive IPV will develop immunity when compared with/to the 10 to 30 per cent when OPV is used.
The higher the injectable polio vaccine coverage, the lower the risk. Hence, routine immunisation coverage in States like Uttar Pradesh and Bihar must be stepped up for IPV to become effective.
“In the beginning of this year only 64 per cent of children were fully immunised. It will reach 82 per cent by the March 2016. Of the 9 million children who were not fully immunised, 40 per cent have already been covered and another 10 per cent will be covered by March 2016,” said Prof. Ramanan Laxminarayan, Vice President — Research and Policy at the Delhi-based Public Health Foundation of India. He established the Immunization Technical Support Unit that supports the immunisation programme of the Ministry of Health and Family Welfare.
India imports inactivated polio vaccine injections at a cost of $2 per dose. Since wild polioviruses are the raw material for IPV, no Indian manufacturer is allowed to make IPV in India. Companies now using biosafety level 3 facilities for IPV manufacturing will move to biosafety level 4 once wild polio is eradicated globally. After that all, OPV will be discontinued and IPV will remain the mainstay.