Updated: September 3, 2015 5:12:05 am
The Injectable Polio Vaccine (IPV) is part of the global endgame strategy for eradication of polio. IPV will become part of the universal immunisation programme (UIP) in phases from November. The decision to introduce IPV was taken over a year ago, after the National Technical Advisory Group on Immunisation (NTAGI) recommended that India should follow up on its polio-free status by introducing the injectable vaccine.
Does this mean that the oral vaccine is not effective?
Far from it. It was the oral vaccine, administered through the pulse polio programme that focussed on reaching out to all children through a door-to-door campaign and Polio Days, that ensured India eliminated the wild polio virus, and earned WHO certification in March 2014. 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. Three years of no infection is essential for certification.
Watch Video: Explained: Polio and Introduction Of Injectable Vaccine
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How do oral and injectable vaccines differ?
A vaccine introduces a pathogen in the body in regulated doses that causes mild or no infection, but leave its trace on the immune system by creating what is known as ‘memory’. The next time the body is exposed to that pathogen, this memory helps it build a swift and potent immune response. 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.
Is the injectable vaccine more effective?
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. It is not common — about 1 in every 2.7 million first doses of the vaccine — and is linked to lack of immunity. Only about 44 cases have been reported in the country so far — nearly all of them cases of infection by the P2 virus, which is said to be the most virulent. P2 was also the first variant to be eliminated — the last case having been reported from Aligarh in 1999. It is even more rare for a virus from the vaccine to mutate and start circulating — such a virus is called Vaccine Derived Polio Virus (VDPV)
Why is the injectable vaccine essential for polio eradication?
Eradication requires cases of both wild and vaccine derived polio infection to be zero. Meaning, there is no trace 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 country) would lose the status immediately, and will have to start from scratch. India is in a particularly precarious position because it shares a border with Pakistan, one of the only three polio endemic countries in the world. That is why it is important to eradicate the virus.
Will the oral vaccine be discontinued?
No, for now 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.
Can India switch to an IPV only regimen?
It will be very costly. IPV costs a dollar a dose. For India’s 27 million birth cohort, and accounting for wastage during transportation, storage etc., 40 million doses are required for a single shot per infant. For the first year, the international vaccine alliance, GAVI, will provide material support. It would require a commitment of Rs 200-250 crore from the government — and triple that for three doses per child like in the case of oral vaccine.
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