World Polio Day: India is not truly free from polio until it beats the vaccine derived virus
In India, there are 50 detected cases of the virus that was derived from the oral polio vaccine.
The certification of polio eradication is conducted by WHO regions. The SEAR (South East Asia Region) countries were declared Polio-Free in 2014, three years after the last case of wild poliovirus infection, detected in the West Bengal India. Since then no wild poliovirus cases have been detected in India and the country is no longer a high focus or polio-endemic country as per the GPEI (Global Polio Eradication Initiative) of WHO.
India accounted for nearly half of all cases of polio in the world till as recently as 2009, and was considered one of the most difficult places in the world to eradicate Polio.
Though, India is a wild, poliovirus, disease-free country currently. But, the cases of Vaccine Derived Polio Virus (VDPV) disease, (around 50 cases documented by India lauded AFP surveillance system) can be seen. The emergence of VDPV disease is a known risk of OPV vaccination, where the weakened live virus given as vaccine in OPV start becoming virulent and thus give rise to the disease in a few children among the lakhs that were vaccinated with it. There is a dire need to focus on getting more and more children vaccinated with IPV, which not only poses no risk of VDPV but also give 99 percent protection from wild polio and VDPV disease.
Until all the children in the country are not vaccinated with IPV, the risk of polio resurgence either due to importations from neighbours (Pakistan and Afghanistan, the only two polio-endemic countries in the world now) or from VDPV will be there.
Polio is nearly 100 percent preventable
There are two types of vaccinations that work against poliovirus, namely inactivated poliovirus (IPV) and oral poliovirus (OPV).
The injectable inactivated poliovirus vaccine (IPV), protects almost all children (99 out of 100) who get all the recommended doses. For best protection, children should get four doses of polio vaccine.
The oral OPV is given in UIP (Universal Immunization Programme) of India, offers somewhat low protection for an Individual (~90 percent) but much better protection for the whole community, due to its gut immunity profile. It helps in breaking the transmission of disease from one infected individual to another, thus it played huge role in making India Polio- free by Pulse Polio Immunization.
However, for Indian children to stay 100 percent free from polio, IPV has to emerge as the dominant vaccine in routine immunization.
In fact, the latest Indian Academy of Pediatrics vaccination guidelines recommends that children should get four doses of IPV at the following stages, 6 months, 10 months, 14 weeks and 18-24 months. In addition OPV is to be administered orally at birth, 6 months, 9 months and between 4 years to 6 years.
How do polio vaccines offer protection?
Oral Polio Vaccine or OPV consists of a mixture of live attenuated strains of polioviruses of three (now only two OPV 1 and OPV 3,) different types of serotypes. These viruses mimic the immune response of the actual polioviruses, but with a reduced ability to spread and affect the central nervous system. After the administration of the vaccines, the body produces antibodies in the blood to fight against these viruses. When a person gets actually infected, the antibodies are already present in the body to prevent the progression of the infection.
OPV vaccines also produce a local immune response in the lining of the mucous membrane of the gut which is the primary site for multiplication of poliovirus. It is because of this gut immunity that OPV has been the preferred vaccine in the immunization programmes of resource-constrained countries such as India because it offers a chance to break the transmission to other children in the community
IPV or inactivated poliovirus vaccine is produced from wild-type poliovirus strains or three the three serotypes that have been killed with the help of formalin. This vaccine is in the form of an injection and can be administered in combination with other vaccines as well.
What's next for Global Polio Eradication?
Poliovirus 2 and 3 have been eradicated globally. There are only two polio-endemic countries in the world now. So the focus for the final win against polio cannot waiver now. The last leg of the war includes securing good immunization coverage for stopping VDPV disease from gaining hold, especially of IPV, eradicating poliovirus 1 and continuing good surveillance.
Dr Binita Priyambada is a senior consultant at Medical Team at Docprime.com
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