India’s fight against polio is expected to receive a boost with the Union government, at last, deciding to introduce Injectable Police Vaccine (IPV), in its drive to eradicate the dreaded crippling and potentially fatal viral disease that mainly affects children under the age of five. IPV will become part of the universal immunization programme (UIP) in the country, in phases from November. The proposal for introduction of IPV, was pending before the government for the last over two and a half decades.
In fact, Polio Immunization Mission in 1988 assessed Oral Polio Vaccine (OPV) and Injectable Polio Vaccine (IPV), Indian research revealed high efficacy of IPV (even with only two doses) and dismal performance with three doses of OPV. It was pointed out that with IPV no child had ever developed polio after three doses – even two doses immunized nearly 100 per cent if even eight weeks apart. On the other hand, it was pointed out that OPV was incompatible with eradication. Self-sufficiency of IPV was vehemently recommended, to which end, the Ministry of Science and Technology established a public sector company at Gurgaon, with France transferring the required technology for operation of the plant. But the Ministry of Health scuttled the project by refusing to licence IPV. In the same year (1988), a private company successfully manufactured IPV combined with DPT, which, experts say, is an ideal vaccine for polio, but that too was scuttled by the Ministry of Health.
During the early 1990s, the number of cases declined, but the proportion of polio cases occurring among vaccinated children increased. The country faced with the challenge of fighting the Vaccine-derived Polio Virus (VDPV) rather than the wild virus itself. Simply put, the small quantity of the weakened polio virus present in the oral polio vaccine (to activate immune response) was causing polio to vaccinated children. But fortunately, from 2009 to 2011, there has been a drastic decline in the number of polio cases. The last case of infection by the wild polio virus – which means virus circulating in the environment, was reported from West Bengal in January 2011.
In March 2014, the World Health Organizations (WHO) officially certified India along with 10 other Asian countries free of polio, after a panel of experts verified that the countries went three years without reporting a single new case of the dreaded disease. The certification has confirmed one of India’s biggest public health success stories, accomplishing something once thought impossible, thanks to the massive and sustained immunization programme involving thousands of health workers who have worked with government and non-government organizations, civil society backed by WHO, UNICEF, Rotary International and Global Polio Eradication initiative.
The Injectable Polio Vaccine (IPV) is part of the global endgame strategy for eradication of polio. In India, the decision to introduce IPV was taken by the Union government over a year ago, after the National Technical Advisory group on Immunization (NTAGI) recommended that India should follow up on its polio-free status by introducing the injectable vaccine, as a more effective measure to ensure that no strain of polio is imported to the country from outside.
According to experts, there is significant difference of effect in injectable and oral vaccines. The oral polio vaccine is made up of attenuated virus – virus that is rendered nearly incapable of producing an infection, but which retains its ability to trigger an immune response. The injectable vaccine, on the other hand, is made up of heat-killed virus that cannot, under any circumstances, cause the disease because the pathogen is not alive – but can produce memory needed for immunity.
In terms of immunogenicity, or the ability to trigger an immune response, the oral and injectable vaccines are comparable. Both contain all three strains of the virus – P1, P2 and P3. However, because in the oral vaccine, the virus is attenuated and not killed, there remain some chances of vaccine-derived polio disease.
Eradication requires cases of both wild and vaccine derived polio infection to be zero. Meaning, there is no trance left of the virus anywhere in the world except in controlled situations in laboratories for future contingencies (smallpox is an example). Injectable vaccine is required because oral vaccine leaves a tiny chance of vaccine derived infection. Also, polio-free status is not irreversible. Should a case of wild polio infection arise, India (or any other country) would lose the status immediately, and will have to start from scratch. Injectable and oral vaccines will continue simultaneously, with the injection being given at 14 weeks, along with the third dose of the DPT vaccine. The three doses of oral vaccine will be given as per schedule. But from April 2016, India will shift to the bivalent oral vaccine – one which has only P1 and P3 – instead of the trivalent one. P2 is being removed to counter its propensity to manifest as a vaccine derived infection – and the gap will be filled by IPV, which has killed viruses of all three strains.
There is no room for complacency. The WHO has advised India to maintain sensitive surveillance and ensure high childhood immunity against the wild polio virus, as this is vital to ensure that no strain of polio is imported to the country until eradication is attained worldwide.
(The writer is a freelance journalist)
