By Nithin Sridhar
Health Minister JP Nadda launched India’s first injectable inactivated polio vaccine (IPV) on Monday. This marks the beginning of the shift from purely orally administered polio-vaccines or Oral Polio Vaccines (OPV) to a combination of dosages of OPV’s and IPV’s.
This is indeed a welcome move in the global fight against polio eradication.
One of the major disadvantages of OPV usage is that there is a chance that it leads to vaccine-associated paralytic poliomyelitis (VAPP). Studies have shown that one child out of every 2.4 million dosages of OPVs administered will suffer from VAPP.
This disadvantage can be overcome by the administration of IPV dosages. IPV was developed by Dr. Jonas Salk in 1955. IPVs consist of killed poliovirus strains (as against live attenuated polioviruses in OPVs) of all three poliovirus types which are then used as vaccines. Hence, they produce antibodies in the blood that provide immunity against all three poliovirus types resulting in protection against VAPPS as well. Further, IPVs are considered very safe and efficient and there are no major side-effects.
This is not to say that, IPVs have no disadvantage. For a long time, polio eradication programs were using OPVs alone because IPVs were observed to be weak in providing intestinal immunity. Hence, if a person immunized with IPV becomes infected with wild poliovirus, then the virus can still multiply inside the intestine and come out in the feces resulting in its continued circulation. But, a recent study shows that, when IPV is used in combination with OPV dosages, then IPVs will boost intestinal immunity.
Thus, World Health Organization (WHO) no longer recommends OPV alone vaccination against polio. It recommends usage of at least one dose of IPV in countries which is using OPV only vaccinations. In polio endemic countries, it recommends usage of 1 OPV birth dosage, 3 OPV dosages and 1 IPV dosage. In countries with high immunization cover and low chances of importation of wild polio viruses, but with a significant VAPP concern, WHO recommends an IPV–OPV sequential schedule. It recommends IPV only vaccination only in those countries which have low importation as well as transmission risks along with very high immunization coverage.
Hence, India’s move in introducing IPVs is in sync with WHO recommendations. This step will go a long way in preventing VAPP and ensuring complete polio eradication from the world.
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