As part of the national immunisation programme, Municipal Corporation of Greater Mumbai (MCGM) has started giving injectable polio vaccine (IPV) along with bi-valent oral polio vaccine (OPV) to comply with the Union health ministry’s mandate to build population immunity.
The health ministry’s polio immune strategy which aims to make a switch over from trivalent oral polio vaccine to bivalent oral polio vaccine in a phased manner envisages to completely stop oral polio vaccination and switch to IPV by 2020.
According to experts, this will help accomplish the switch over from trivalent OPV to bivalent OPV effectively and will gradually be scaled up until the OPV is completely stopped.
The trivalent OPV currently in practice covers three viruses, of which disease caused by type 2 virus has not been seen since 1999.
According to the World Health Organization (WHO), routine immunisation with OPV must cease after the eradication of polio virus because of the danger of outbreaks of circulating vaccine-derived polio virus and the risk of vaccine-associated paralytic poliomyelitis (VAPP).
In the regions of the world in which wild type polio virus has been eliminated, moving to an IPV or IPV/OPV sequential schedule will reduce or eliminate the risk of VAPP and outbreaks of circulating vaccine derived polio virus, as well as increase the likelihood of countries agreeing to stop administering OPV after eradication is achieved.
Oral polio vaccine is a live attenuated vaccine produced by passage of polio virus through non-human cells at a sub-physiological temperature, which causes spontaneous mutations in the viral genome.
OPV is superior to IPV in ease of administration, and there is no need for sterile syringes, as with IPV. OPV also provides longer immunity than does the Salk vaccine. However, OPV has strict requirements for transport and storage, and this is a big problem in some hot or remote areas.
A major concern about OPV is its ability to revert to a form that can cause paralysis. Outbreaks of vaccine-associated paralytic poliomyelitis have been reported in many countries of the world.
In 2006, 1600 cases of vaccine-induced polio occurred in India, according to the Indian Medical Association Sub-Committee on Immunisation's report on the Polio Eradication Initiative. These cases were reported during repeated mass-immunisation campaigns in which repeated doses of OPV were administered.