Eradicating Polio: It's Feasibility in Near Future?

Transcription

1 J. Commun. Dis. 40 (4) 2008 : Eradicating Polio: It's Feasibility in Near Future? Singh Prem*, Das JK*, Dutta PK* Abstract Continuous wild poliovirus transmission despite 2 years of intensive surveillance has raised serious questions about the feasibility of polio eradication programme with current strategy in near future. At present most of the cases are confined to four endemic countries, which are causing sporadic outbreaks in non-endemic areas. India has experienced a significant increase in number of cases reported in 2006 compared to previous year. Outbreaks originated in western UP which was due to the accumulation of susceptibles between the last outbreak in 2002 and early Substantial improvement has been observed in strategies of polio eradication but still there are gaps in the programme implementation which needs immediate attention so that goal of polio eradication can be achieved at the earliest opportunity. Even though there are many issues but there are also many factors, which favour polio eradication. These factors include new tool in form of m OPV, natural immunity due to recent outbreak, limiting international spread of polio, new researches to guide programme in right direction, political commitments from endemic countries, etc presents the best opportunity ever to interrupt wild polio virus transmission which will lead to global eradication of Polio. Since global eradication is within sight, it is scientifically possible to eradicate the disease in near future. Key words : Wild Poliovirus, Oral Polio Vaccine, Monovalent OPV, Trivalent OPV, AFP Surveillance, Supplementary Immunization Activity (SIA), Routine Immunization, VAPP, VDPV, Compatible, Adequate stool, NPEV, Disease Outbreak etc. Following the success of world wide st eradication of Small Pox, the 4 World Health Assembly in May 88, committed Global Eradication of Poliomyelitis. F o l l o w i n g t h i s d e c i s i o n b y W H O considerable progress has been made towards interrupting the transmission of wild polio virus globally. As a result of the Global Polio Eradication Initiative (GPEI), which is the largest international public * National Institute of Health & Family Welfare, Munirka, New Delhi. Correspondence to : Dr. Prem Singh, Deptt of Epidemiology, MCHA, NIHFW, Munirka, New Delhi, Ph: , drprem76@rediffmail.com

2 226 Singh Prem et al health effort till date, the number of Polio endemic countries world wide has declined from over 25 in 88 to only 4 in 2006 (Nigeria, India, Pakistan and Afghanistan). The disease burden has also been reduced by more than % since 88. Three WHO regions have already been certified free from indigenous wild polio virus i.e. Region of America (4), Western Pacific Region 2 (2000), and European Region (2002). Circulation of Wild Polio Virus (WPV) continues despite 2 years of intensive efforts, which has raised the question about the feasibility of global polio eradication programme with the current strategy. Transmission is still continuing only in a few localities which act as sources for outbreaks elsewhere. The greatest challenge is in India, where transmission has persisted in a few western districts of Uttar Pradesh and Bihar despite high vaccination coverage. An effort to eradicate polio is based on 3 four key strategies: ; (a) To achieve and maintain high level of routine immunization coverage of OPV, (b) mass immunization campaign, (c) Acute Flaccid Paralysis (AFP) Surveillance and (d) mopping Up operations. Experience in several of the world's WHO Regions, where polio has been eliminated, has demonstrated that the recommended strategies are highly effective and that the global eradication of polio is feasible. Technical feasibility of Polio Eradication Eradication of the disease depends on disease epidemiology and the tools available to combat it. Absence of a non-human reservoir and brief survival in environment make it suitable for eradication. Availability of an effective intervention and delivery strategy in form of two excellent vaccines (IPV and OPV) to interrupt transmission of Polio is key for eradication. However IPV appears to have interrupted poliovirus transmission only in three industrialized countries in northern Europe (Finland, Netherlands and Sweden). On biological and technical basis, OPV was selected as the vaccine of choice for the eradication initiative because it induces secretory intestinal immunity which spread from vaccinees to their close contacts, thereby also protecting some unimmunized 4 children. Its low cost and oral administration route proved to be additional characteristics that made this vaccine much more suitable for use in eradication strategy. Practical diagnostic tools with sufficient sensitivity and specificity to detect levels of infection also can lead to transmission through current system of AFP surveillance. The technical feasibility of eradicating wild-type poliovirus was confirmed in October when the last case of paralytic polio due to wild poliovirus type 2 ( of 3 types) was detected elsewhere in the world. By 2002, the feasibility of eradication was reaffirmed by certification of eradication of all 3 wild poliovirus types in 3 of the 6 WHO 4 Regions. The successful outcome of Small Pox eradication made the epidemiologists think for polio eradication as there are many similarities in epidemiological and various technical factors for both the diseases. But there are few factors, which make polio eradication more difficult than small pox eradication. Firstly in small pox, sub clinical cases were not transmitting the infection whereas on the other hand in polio 000 sub clinical cases for each polio case exist which also transmits poliovirus. Vaccine for small pox was one-shot vaccine for complete protection, whereas in polio there are cases even after more than 0 doses of OPV immunization. Small pox vaccine was heat stable and OPV is heat labile vaccine which requires proper cold chain system. Most of the cases with high OPV doses raised questions to be answered in terms of

3 Eradicating Polio : It's Feasibility in 227 strategies and efficacy of vaccines, which need to be answered soon for achieving polio eradication. Global and Indian Scenario Globally there are four endemic countries, which never achieved interruption of polio transmission and continue to be threat for other countries. These include Northern Nigeria, Afghanistan and Pakistan border 5 areas and western UP & Bihar in India. In 2005 and 2006 globally there were more than 00 polio cases with maximum number in Nigeria. In 2008 global cases reported are 423 till May 2008 with 52.5%of cases in India and 40%in Nigeria. These endemic areas are responsible for causing sporadic outbreaks in the non-endemic countries. In 2007 total global cases were 32 with 872 cases alone in India, mostly of P3 type. (WHO Headquarter data as on 3th May 2008) 26 countries were re-infected with importations of poliovirus since 2003, which is a major concern for the eradication programme. Outbreaks in non-endemic areas are costly, stressful and frustrating, which also lead to distracting priorities from endemic countries. But experience shows that if outbreaks are responded effectively, they can be controlled. Nigeria especially in northern part of the country is having intense transmission in key states. In 2006, northern Nigeria continued to account for the majority of global cases. Problems in Nigeria occurred because large proportion of children were not accessible due to socio political objections which were mainly due to misconceptions and Nigeria stopped polio immunization activities for 7 sometime. Expert Review Committee for Polio Eradication (ERC) in Nigeria endorsed a strategy of 'Immunization Plus Days' (IPDs) in March Launched by the new management of National Polio Immunization in May, IPDs offer other antigens and health interventions to communities in addition to mopv. Since the introduction of IPDs, the proportion of children in northern states who had never been immunized was reduced to an average of 20% (from more than 50% at 5 end-2005). In Afghanistan and Pakistan insecurity led to large proportion of children not being immunized with vaccine. Hence polio transmission is limited to mobile or socially conservative communities and disturbed areas, which are mainly limited to border 6 areas of Afghanistan and Pakistan. India has also experienced a significant increase in new cases in 2006 compared to the previous year (676 cases in 2006, compared to total 66 cases in 2005). Nearly half of these cases occurred in Moradabad and adjacent districts in western U.P. The outbreaks originating in western Uttar Pradesh is on the wane in its epicenter but has spread to the eastern parts of the state and several other polio-free areas. India not only had ten times more cases in 2006 as in the corresponding period during India's share of the global burden of the disease had also risen to 30%, in contrast with only 3% of global cases 8 at the same time in When world is working towards polio eradication; there was set back in India Western UP and Bihar with 548 and 6 wild virus cases in 2006 respectively are major reservoirs of disease and pose threat for the global polio eradication initiative. A number of factors are responsible for continuous transmission in these areas which need to be looked into. Currently in 2008 India were having 22 wild virus cases in 55 districts, with 225 P3 cases and only 4 P cases however no P case in key districts (Moradabad and adjacent districts) of western UP for past one and a half

4 228 Singh Prem et al year. In 2007 there were 873 cases in India with only 83 P cases and rest were of type P3. F a c t o r s r e s p o n s i b l e f o r o n g o i n g transmission in India Increase in P3 cases were due to the change in Polio Eradication strategy i.e. to focus on only P cases in India by using monovalent P vaccine in order to eradicate P poliovirus first and then attack type P3 which is easy to eradicate. The continuous transmission in Western UP is due to multi-factorial reasons, which are high population density, poor health service delivery infrastructure, poor environmental sanitation and inadequate Routine immunization coverage (with only 23% of fully immunized children according to NFHS-3). Extreme high Non Polio Entero Virus rates also show that there is favourable environment for wild polio virus circulation which may be causing probable interference with OPV. Persistence of transmission in Western UP is also associated with poorer Supplementary Immunization Activity (SIA) mainly due to a large number of missed houses and high immunity gap among cases and children with less than 2 years of age in affected areas. On the other hand along with poor SIA indicators Bihar has also problems of migratory population, which are not only having less immunization coverage but also responsible to spread of wild virus to nine other states. The most common reasons of outbreak in 2006 was due to the accumulation of susceptible population, between the last outbreak in 2002 and early These susceptibles were accumulated due to gaps in OPV coverage & less efficacy of trivalent OPV in key areas. Current issues in Polio Eradication Issues related to Vaccine There are number of questions raised on vaccine quality as there are large number of cases occurred even with high immunization status. OPV used in India during SIAs is procured by UNICEF from WHO prequalified manufacturers, and WHO recommend pre-release testing of OPV of all batches, which further monitor vaccine potency. In the field, Vaccine Vial Monitor (VVM) also helps to identify loss of vaccine potency due to heat. But effectiveness of VVM especially chemical used in it is the important factor, which was never explored and requires urgent attention of policy makers. In view of the recent concerns regarding vaccine potency, 27 samples from Moradabad/ Sitapur/ Hardoi, manufactured between Dec'05 and May'06 were subjected for post-release testing in May/June 2006; 00% samples were found satisfactory. 370 samples collected from field, during September 2006 round were also found to be potent. Vaccine-associated paralytic polio (VAPP) is a rare adverse reaction following live OPV. The risk of VAPP is not equal for all OPV doses in the vaccination series. The risk of VAPP is 7 to 2 times higher for the first dose than for any other dose in the OPV 0 series. The overall risk of vaccine associated paralytic poliomyelitis is extremely low and has been found as one case occur per 2.5 million doses of trivalent OPV, with the highest risk being associated with the first 3 dose. In most of the countries, population immunity to poliovirus is maintained only by immunization. It has been observed where polio vaccine coverage rates have declined but OPV use continues conditions may arise in increase of person-to-person spread of

5 Eradicating Polio : It's Feasibility in 22 Vaccine Derived Polio Virus (VDPV). It is due to prolonged circulation of Sabin virus among children with low OPV coverage, which result in poor herd immunity. Few outbreaks associated with VDPV occurred in Hispaniola in , Philippines in 200, Madagascar in with largest outbreak in Indonesia in 2005 with 46 cvdpv cases. But these outbreaks were controlled with OPV only. Therefore high immunity in community with OPV reduces the risk of cvdpv. But in post eradication strategies with cessation of OPV, cvdpv can pose severe threat to the programme, which needs to be addressed in future. Large Number of P3 cases Current focus is to eradicate P polio virus first by using monovalent P vaccine. Due to this there is huge rise in P3 cases in India, as children are not immunized against P3 virus. It seems that India is near to eradication of P cases with only 4 P cases for whole of the country in 2008, which is lowest ever occurrence of P cases. But when country will switch over to P3 eradication by giving only monovalent P3 vaccine, there will be risk of importation of P virus from other endemic countries as children will be lacking immunity against P virus, thus leading to P outbreak. This risk should be kept in the mind of policy makers, so that attack on P3 does not lead to lack of immunity for P virus. High routine immunization coverage with trivalent vaccine is therefore utmost important tool for eradication of both these viruses. Acute Funding Gap In early 2007, however, the Global Polio Eradication Initiative funding gap became particularly acute due to (a) an increase in the number of polio campaigns to fully exploit the benefits of the new mopvs, and (b) a decrease in multi-year pledges by donors funding Gap is equal to US$ 540 million. Efforts are being made to reduce this funding gap by increasing the domestic and international financing for polio eradication activity. Compatible cases : Cases with inadequate stool specimens and having residual weakness, who have died or are lost t o f o l l o w - u p u n d e r g o a d d i t i o n a l investigation and these findings are utilized for review by the National Expert Review Committee (ERC). This committee comprises of highly skilled pediatricians, neurologists, virologists and epidemiologists who examine all the evidence and make a judgment on the most likely diagnosis. The ERC classifies the case as compatible with polio or discarded as non-polio AFP. Polio-compatible cases may be viewed as evidence of a failure of surveillance, and serve as a reminder that all efforts must be undertaken to ensure that adequate stool specimens are collected from 3 every AFP case. Poor Routine Immunization coverage of OPV in endemic countries is a major issue in not eradicating polio till date. Almost in all the endemic areas RI status is very poor. Though there is a marginal increase seen now especially in western UP and Bihar region of India but still country is far from required immunization coverage in these areas. This clearly shows that there are failures in one of the most important strategies of polio eradication. Gap in SIA activities is the reason that the country is not able to reach every child in endemic countries. Reasons include large number of missed houses in areas with polio transmission and high immunity gap especially in younger children. Resistance among community is also a set back for this programme. Most common reason for resistance is misconceptions among community that this vaccine causes infertility

6 230 Singh Prem et al in children; vaccine is made from pigs and also vaccine can cause severe illness which can lead to death of the child. These old misconceptions still persist in the minds of community members though huge efforts on social mobilization have been attempted for past so many years. Non Polio Entero Virus (NPEV): Most of the districts reporting repeated WPV cases have also reported more than 40% AFP cases 0 associated with NPEV. It may be possible to link this to poor environmental sanitation and poor immunity status of the vaccinated children. Western UP region are having very high NPEV rate and this area is continuing wild virus transmission also. Therefore this factor should be explored whether it is causing high interference with OPV leading to low immunity with OPV though administration of adequate number of doses. Poor health Infrastructure in these areas : These endemic areas are not only poor in eliminating polio transmission but also having poor health infrastructure and unsatisfactory health activities. Shortage of Medical Officers and other paramedical staff in these areas is also an important issue. Importation of Wild Virus in nonendemic countries : 26 countries are reinfected with importations of poliovirus since 2003, which was a major concern for the programme. (GPEI). Outbreaks in nonendemic areas are always costly, stressful and frustrating, which also lead to distracting priorities from endemic countries. The number of cases ranged from in Eritrea to 478 in Yemen. But experience shows that if outbreaks are responded effectively this can be interrupted. As a result, re-infected countries only accounted for 6% of all polio cases in 2006, down from more than 50% of 2 cases in These cases originated from India (8%) and Nigeria (82%) which indicate that there is a urgent need to control polio in the endemic countries because they can be source of 5 importation in near future. Cases in higher age group as in Namibia : A new threat to the eradication programme emerged in Namibia in early 2006, when 20 cases of polio were reported in people aged between 4 to 5 years. This incidence has raised a number of epidemiological issues since vaccination is carried out in less than 5 years old children 2 only. Poor Environmental Sanitation and Personal Hygiene : Poor environmental sanitation and overcrowding have helped in the continued transmission of polio virus in certain poor countries in Asia and Africa, despite massive global efforts to eradicate 3 polio. Several of the 'resistant' pockets in UP and Bihar, which are now being called reservoir of WPV, particularly the urban and peri-urban areas, also present abysmally poor sanitary conditions. Thus improving environmental sanitation and hygiene should be the foremost priority. Factors favoring Polio Eradication Natural immunity due to recent outbreaks : There were 34 cases in 8 in India and then there was decline in number of cases and in 200 cases reported were as low as 268. But after four years i.e. in 2002 there was an outbreak in UP and number of cases reached 600. Thereafter cases declined in next year and reached all time low in 2005 with just 66 cases. There was a cyclic upsurge in 2006 with outbreak in western UP and total cases reached to 676. Outbreaks of polio in 2006 was due to the accumulation of susceptibles between the last outbreak in 2002 and early 2006 and this was due to large gaps in OPV coverage. Decline after each outbreak is due to natural immunity caused by the outbreak. So there is an opportunity for epidemiologists to eradicate polio if there is a

7 Eradicating Polio : It's Feasibility in 23 good quality programme and natural immunity will give additional advantage to reach zero status. Fall in P cases : There is rapid decline in P cases in India after extensive use of monovalent P vaccine. Western UP has shown only P case during last one and a half years, which was the main P prevalent area earlier in India. Decline in number of missed houses is an indicator of a good SIA activity and now things are improving in the affected regions with fall in number of missed houses especially in western UP. New Tool in form of monovalent OPV : A recent study confirms that new polio vaccines ('monovalent OPVs' or 'mopvs'), developed by an extraordinary publicprivate partnership in , substantially enhance the impact of polio campaigns. These vaccines provide more than double child's protection against the specific type of polio present in a country, as compared with 4 the traditional trivalent OPV. Limiting International Spread of Polio: WHO and UNICEF are assisting various re-infected countries to implement rapid responses to polio outbreaks. WHO will also assisting in updating national immunization policy to reduce the risk of polio importation. Polio and the International Health Regulations, 2005 : In May 2005, the World Health Assembly (WHA) adopted the International Health Regulations 2005 (IHR 2005). Coming into effect in 2007, the IHR, 2005 identifies four diseases (Smallpox, SARS, Avian Influenza of pandemic potential and circulating Polioviruses) of which any occurrence must be reported 6 internationally. Researches to guide Programme : It is very important to conduct operational research activities related to programme implementation and the findings of these research studies will help to move the programme in right direction. Most important aspect of research is related to seroconversion survey and ICMR has already planned to have a rapid research in high-risk areas. Researches related to introduction of IPV are also important so that if mopv does not deliver as per expectations, health administrators should be prepared with alternative model. Israel has already eliminated polio in Gaza strip by using 5 combination of OPV and IPV. This is a success story, which is to be verified in Indian conditions. Enhancing the Safety of Polio Workers & Volunteers : WHO, UNICEF and relevant international stakeholders should ensure the safe passage of vaccinators to reach all children in insecure areas and areas of active conflict. Sensitivity of AFP surveillance should remain high so that it is possible to detect all the potential areas of polio transmission, which will guide necessary action to control the disease. EPILOGUE Since the launch of the Global Polio Eradication Initiative, an estimated five million people who would otherwise have been paralysed are walking today; thanks to oral polio vaccine received when they were very young children. Unless polio is eliminated in India and Nigeria, Global Eradication cannot be achieved. Global polio eradication depends on the political commitment and good governance of these affected four countries, which have never experienced cessation of polio transmission: Nigeria, India, Pakistan and Afghanistan. More than 0 million children will be paralysed in the next 40 years if the world fails to capitalize on its US$ 4 billion global 8 investment in Polio eradication.

8 232 Singh Prem et al With polio geographically more restricted than ever before, and equipped with new-generation tools and strategies, the world now has the best-ever opportunity to eradicate polio once for all, providing there is a collective global will and sustained political commitment from the highest levels. The key to success will be full implementation of the targeted new approaches, high-quality immunization and mopping up operations and the continued support of donors, most notably in urgently filling the global funding gap presents the best opportunity ever to interrupt wild poliovirus type by using new efficient tool in form of mopv and by accelerating rounds to rapidly immunized young children in high risk areas. Routine immunization strengthening is a key to eradication and this will not only strengthen health system in the time when SIA rounds will be reduced but also prevent from other vaccine preventable disease and make a way for eradication of Measles after Polio eradication. This is also a time to take advantage of natural immunization from recent outbreaks and not allow in loosing this opportunity. REFERENCES. Global Polio Eradication Initiative, July 2007, 2. Smith J, Leke R, Adams A and Tangermann R, Certification of polio eradication: process and lesson learned. Bulletin of World Health Organization. 2004; 82(): MOHFW, New Delhi, Surveillance of Acute nd Flaccid Paralysis, Field Guide, 2 edition, January 2000; 2, Aylward RB, Hull HF, Cochi SL, Sutter RW, Olive JM and Melgaard B. Disease eradication as a public health strategy: a case study of poliomyelitis eradication. Bulletin of World Health Organization, 2000, 78(3); Venczel Linda, Update on the Global Polio Eradication Initiative, Global Immunization Division CDC/NCIRD, Annual Report 2006, Global Polio Eradication Initiative, World Health Organization Centers for Disease Control and Prevention. Resurgence of wild poliovirus type transmission and consequences of importation into 2 previously polio-free countries, Morbidity and Mortality Weekly Report 2006; 55: Global Polio Eradication Initiative, December 2006, National Polio Surveillance Project: GOI & WHO, Location of Poliovirus, as on 3th May 2008; 0. Mittal Onkar, Sathyamala C. Background information note: Global Polio Eradication Initiative in India , IMA Conference, Final Draft 4th May, Kew Olen M, Wright Peter F, Agol Vadim I, Delpeyroux Francis, Shimizu Hiroyuki, Nathanson Neal and Pallansch Mark A. Circulating vaccine-derived poliovirus: current state of knowledge. Bulletin of World Health Organization. 2004; 82(); Lahariya Chandrakant, Global eradication of polio: the case for finishing the job. Bulletin of World Health Organization, 2007; 85(6); Nelson's Text Book of Pediatrics- 7th edition. 4. Grassly NC. Protective efficacy of a monovalent oral type poliovirus vaccine: a case control study. Lancet. 2007; 36(570): Goldblum N, Gerichter CB, Tulchinsky TH, and Melnick JL, Poliomyelitis control in Israel, the West Bank and Gaza Strip: changing strategies with the goal of eradication in an endemic area. Bulletin of the World Health Organization. 4; 72(5): The World Health Organization, The Case for C o m p l e t i n g P o l i o E r a d i c a t i o n,