Dual use of IPV to tide over shortage
Due to shortage of Inactivated Polio Vaccine (IPV) globally, India and a few other countries are stretching the supply of the vaccine to cover all children. To tide over the shortage, children in Puducherry, Andhra Pradesh, Karnataka, Kerala, Maharashtra, Odisha, Tamil Nadu and Telangana will get two doses administered intradermally. This is being done despite the vaccine being licensed only for intramuscular use.
Poliomyelitis (polio) is a highly infectious viral disease which mainly affects young children under 5 years of age. The virus is transmitted through faecal-oral route and multiplies in the intestine to invade the nervous system and cause paralysis. There are 3 types of wild poliovirus strains- type 1, type 2, and type 3. The transmission of type 2 wild poliovirus has stopped since 1999.
In 1988, when the global polio eradication programme was launched, there were about 3,50,000 cases of polio in over 125 countries. The number has now come down by 99% to 74 in 2015 and only Pakistan and Afghanistan remain polio-endemic.
There are 2 types of polio vaccines- IPV (Injectable Polio Vaccine) and OPV (Oral Polio Vaccine). While the IPV, also called as "Salk vaccine"- as it was discovered by Jonas Salk, contains inactivated (killed) poliovirus strains, OPV, or "Sabin vaccine" contains attenuated (weakened) poliovirus strains. Since, IPV is 5 times costlier that OPV, latter is more commonly used against polio, especially in developing countries.
Initially, Trivalent Oral Polio Vaccine (TOPV) which acts against all three types of poliovirus strains- type1, type2, and type3 was used for vaccinations as all the three poliovirus strains were actively causing poliomyelitis. However, TOPV uses inactivated poliovirus which can mutate into virulent forms causing VAPP (Vaccine Associated Paralytic Polio). It can also cause circulating Vaccine-Derived Polio in communities with poor sanitation.
Since type2 poliovirus had already been eliminated in the wild, the use of TOPV was unnecessarily leading to cases where the vaccine itself was causing polio. Although the number was small, 1 in 1.5 million, it was not insignificant. Hence, a switch-over from TOPV to BOPV (Bivalent Oral Polio vaccine) which acts against type1 and type3 poliovirus will help eliminate type2 poliovirus completely.
India along with 155 countries will switch over to the bivalent polio vaccine from the present trivalent polio vaccine on 25th April 2016 as a strategy to end polio in the world. This is being done to eliminate the incidence of vaccine-derived polio virus. Notably, India has been declared polio free and has not reported any polio cases for the last 5 years.
After moving to BOPV vaccine, WHO aims to phase out the OPV and adopt IPV by 2020 to completely eliminate polio from the world.
