POLIO: WHY WE ARE STILL STRUGGLING TO ERADICATE ?
Dr. Vipin M Vashishtha*
Consultant Pediatrician, Mangala Hospital, Bijanor.*
1- Poor efficacy of OPV in Endemic regions ('Vaccine Failure')
Though OPV was the right choice to begin the massive, synchronized global exercise and it did deliver good in restricting the wild poliovirus to certain limited geographical regions. However, it is marred with certain inherent weaknesses like VAPP and cVDPVs. But, the greatest drawback of OPV is its unpredictable immune response in a vaccinee - even after administration of 10 doses; one can not be sure whether the vaccinee developed adequate immune protection or not. For example, in India in 2005, 33% of children with confirmed polio had received 10 or more doses. Historically, it is believed that control of poliomyelitis can be achieved by properly immunizing 80-85% of the population. In some high-risk districts of western UP despite achieving coverage as high as 96.5%, OPV failed to break wild virus transmission and 7.25% children of a study group failed to show seroconversion to any of the three sero-subtypes.

The OPV has geographic variation in efficacy - high in rich, industrialized nation, low in Taiwan, and Oman, lower still in many developing countries due to host (e.g., concomitant infections, malnutrition), programmatic (e.g., cold chain failures) and environmental factors, requiring substantially more does to seroconvert an individual. In the foci of persistent transmission, the efficacy may be the lowest. Low effectiveness and low herd effect - all factors that make the vaccine a poor match to the task of interrupting the transmission of the most transmissible among wild poliovirus, type namely type 1. India, Pakistan, Egypt to some extent Nigeria, provide the toughest challenge to effectiveness of OPV in halting the wild virus transmission. High population density, sub-optimal sanitation, concurrent enteroviral infection, interference among 3 sero-subtypes of sabin viruses, sub-optimal practices of vaccine handling along with tropical climates combine to facilitate the transmission of wild poliovirus.

Hence, OPV was the right 'tool' to start with, but the program initiators failed to anticipate the current shortcoming of the vaccine in final phase of the GPEI, particularly in some most hostile geographic regions. As a result, neither alternate strategy nor other options were envisaged to deal with current imbroglio. Though, monovalent OPV might salvage the situation to some extent, but it is also not devoid of some of the most inherent deficiencies of its precursor. The presumed failure of OPV to combat ongoing transmission of wild virus in endemic countries like India despite using it in its most potent form pose the greatest challenge to the ultimate success of GPEI.
2-Programmatic 'hiccups'
Failure to reach all children below five years of age in some highly endemic regions, suspension of all forms of polio activities in Nigeria in 2003-2004, resistance to OPV among Muslim community in India and Nigeria, poor quality of SIAs, inadequate engagement and involvement of the general community, failure to launch an effective, aggressive IEC, lack of co-ordination amongst enforcing agencies, programmatic fatigue and inertia in most endemic countries are the main factors that halted the swift progression of the initiative.
3-Peculiar epidemiology of Type 1 Poliovirus in Endemic regions
The vast difference in the epidemiology and environmental factors in different parts of the world provided very high forces of wild virus transmission. The strategy adopted in the regions where force of transmission is low did not work in places with high force of transmission such as India, Egypt and Nigeria. Wild polioviruses have been eliminated even in nearly all low-income countries with low or moderate force of transmission with a lesser efforts. However, high density of population, relatively high birth rates and consequent high density of infants and toddlers the most efficient amplifiers and transmitters of WPV, poverty, low literacy, low living standards with poor sanitation and hygiene form a milieu of formidable high force of transmission in endemic countries. Interventions that worked in other poor communities and countries may not be sufficient to over come such exceedingly high force transmission. We failed to recognize this geographic variation in behavior of wild poliovirus especially type 1 and, consequently now facing the prospects of loosing control over the eradication imitative.
4-Neglect of Routine Immunization (RI)
Routine Immunization (RI) is unarguably the weakest link and probably, the most neglected area of the 'four pronged' eradication strategy. The current strategy has put all the emphasis on SIAs. It seems the strategist do not have much faith on the effectiveness of RI and by increasing the frequency of SIAs, they have indeed left nothing for the RI. This is certainly a major flaw. Even if transmission is broken and 'zero polio status' is achieved through high quality SIAs, it is ultimately RI that will determine the 'herd immunity' and will thwart any attempt of importation of the disease in the community. As the recent episode of importation of WPV in to 21 previously polio-free countries shows, the 8 countries following importation with no sustained WPV transmission differed considerably in RI status from 13 countries where transmission following importation was sustained. According to WHO/UNICEF estimate for 2003, the median vaccination coverage with 3 dose of OPV (OPV 3) by 12 months of age in the 8 countries without sustained spread was 83%, compared with a median coverage of 52% in the other 13 countries (P = 0.001). Hence, robust RI would be the greatest deterrent to the greatest threat to polio-free status - the importation of wild viruses! The current status of RI in some of the highly endemic countries is indeed pitiable.
5-Conflict, Social unrest and Accessibility problem
In certain countries like Sudan, Afghanistan, Angola, the conflict among community and political vacuum have already adversely affected the ongoing eradication campaign. Afghanistan, Pakistan, Sudan and Somalia are the few countries where major security risk made accessing all population extremely challenging. Frequent floods in Bihar (India) and fierce resistance by Muslims in northern Nigeria and also made the task of volunteers more difficult.
6-Lack of Foresight and Flexibility
The greatest flaw of the current strategy was almost exclusive and over-reliance on OPV to achieve the goal. The conceivers of the program failed miserably to even anticipate OPV's limitation in final stages of polio eradication in some of the most 'stubborn regions' of the world. Apart from keeping the option of using monovalent OPV in final stages and during post-eradication phase, they failed to devise an alternate strategy to break wild virus transmission where OPV found wanted and quite unequal to the task. The enforcing agencies did fail to anticipate the current scenario in endemic countries where intense, high force transmission of type 1 WPV almost rendered the OPV redundant.
Polio Epidemic in Western Uttar Pradesh
The recent resurgence of polio cases in Western UP is mainly due to epidemic in Moradabad District of Western UP, which can easily be termed as "Polio Capital" of India. This is the most volatile region on earth as far as wild poliovirus transmission is concerned.

The reasons why Moradabad suffered so badly are mainly programmatic/managerial & our inability to reach 100% children aged <5 years in the region. There is no fault with the vaccine though its efficacy is certainly low in these 'hotpots' than in other parts of the country. There was false reporting of immunization coverage in Moradabad district. The vaccinators went in to a sort of a 'secret pact' with resistant families and applied finger mark on target under 5 children without actually administering the vaccine. Hence, everybody was happy; the families, vaccinators and the administrators. Therefore, the actual coverage was in the range of 70-80%, while reported coverage was above 90%.

Another method adopted by some muslim families to avoid polio vaccine was application of some coloring agents/water color on the little fingers of their children. The resistance to OPV, both active and passive amongst underserved muslim families is one of the most significant factors responsible for persistence of the disease in this belt. Hence, a large pool of unvaccinated children, who were shown vaccinated in record, gathered over a period of time and consequently let the virus actively circulate amongst them, which resulted in an outbreak of wild polio this year.

Poor performance by health workers and civil administration where a large number of houses are missed during pulse polio campaign is another reason that contributed to polio epidemic.
Why there is so much of resistance to OPV?
Firstly, there is suspicion amongst the muslim community that the vaccine is contaminated with some 'anti-fertility' agent and Government and western agencies have some hidden agenda and motive to make muslim community sterile. Frequent 'fatwas' from muslim fundamentalist groups have also strengthened this belief. Further, the resisting families take this opportunity to reflect their anguish, anger and neglect to local civic administration and place several demands to the vaccinating teams and officials that to be fulfilled before agreeing to administer vaccine to their children. There are some other factors also responsible for the dismal state of PE in the in reason (vide below). This episode also highlights the "poor governance" and crumbling of civic infrastructure in these few 'hotspots'/regions.
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