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Global poliomyelitis eradication: status and implications
Comment
Global poliomyelitis eradication: status and implications
www.thelancet.com Vol 369 April 21, 2007
wild virus transmission). The cost difference between the posteradication and control scenarios is used to conclude that “we should be willing to invest more than $8000 million to achieve eradication”. The authors conclude that even a policy that included global introduction of inactivated poliomyelitis vaccine (IPV) after the “eradication” of poliomyelitis will, over 20 years, cost less than implementing any of the modelled control strategies. Readers may note that Thompson and Duintjer Tebbens’ use of the phrase “poliomyelitis eradication” for interruption of wild poliovirus transmission is confusing, and exacerbates a semantic problem which has haunted the GPEI since its inception. The termination of wild virus transmission does not guarantee eradication of poliomyelitis disease, considering that OPV viruses are transmissible and are known to revert back to wildtype phenotype.4,10 WHO has recognised this problem and declared that OPV will have to be discontinued if poliomyelitis is to be eradicated.1,2 The essential step of terminating transmission of all OPV-derived viruses remains untested. These two papers provide encouraging insights into the current methods and long-term economics of the GPEI. The demonstration of superior effectiveness of mOPV vaccine adds to the evidence that termination of wild poliovirus transmission is technically feasible, given enough time, continued funding, political stability, and continued political support in the affected areas of the world. The modelled illustration of the financial
Published Online April 12, 2007 DOI:10.1016/S01406736(07)60533-9 See Comment page 1322 See Articles pages 1356 and 1363
The printed journal includes an image merely for illustration Science Photo Library
The Global Polio Eradication Initiative (GPEI) is among the most ambitious programmes ever undertaken by WHO. Begun in 1988, it has made extraordinary progress, reducing the global incidence of poliomyelitis by more than 99%.1,2 Wild poliovirus is now regarded as endemic in only four regions of the world. In Afghanistan and Pakistan, security problems have hampered vaccine delivery. In northern Nigeria, there has been a loss of public confidence in the vaccine, low uptake, and consequent outbreaks which have seeded virus into several other countries. And in the Indian states of Uttar Pradesh and Bihar, the wild virus has proven extraordinarily well entrenched, partly because of low efficacy of conventional trivalent oral poliovirus vaccine (tOPV) in that environment.3 Other problems have arisen that could threaten the feasibility of stopping all poliovirus transmission: the recognition of circulating virus derived from oral vaccine,4 persistent excretion of poliovirus by immunodeficient individuals,5 and difficulties in ensuring containment of all potential sources of reintroduction.6 These difficulties have led to a recommendation that the programme abandons its eradication goal in favour of a control approach.7 Two papers in today’s Lancet provide important perspectives on this debate and on the current stage of the programme. Nicholas Grassly and colleagues analyse recent data from India to compare the effectiveness of a monovalent oral type 1 poliovirus vaccine (mOPV1) with that of tOPV.8 There are problems in inferring absolute vaccine efficacies in such circumstances. But the relative efficacy estimates should be valid, and they indicate that the newer mOPV is more effective than the older tOPV. Let us hope this difference is sufficient to terminate the remaining chains of transmission of type 1 wild poliovirus. Kimberly Thompson and Radboud Duintjer Tebbens use a dynamic model to show that a decrease in immunisation intensity in endemic areas will result in a rapid accumulation of susceptible individuals and many more cases of paralytic poliomyelitis (northern India is used as an example).9 In addition, they argue that both the cumulative number of patients with paralytic poliomyelitis, and the financial costs, that would occur with various control options are higher than with any of four policies suggested for the era after “poliomyelitis eradication” (defined by these authors as interruption of
Coloured transmission electron micrograph of polioviruses
1321
Comment
implications of managing patients with paralytic poliomyelitis and continuing to control poliovirus with supplemental immunisation activities is based on a large number of assumptions, but it supports arguments against abandoning the goal to eradicate wild virus at least. Despite its established efficacy against wild virus, the usefulness of mOPV in combating transmission of vaccine-derived viruses, after the eradication of wild virus, is unclear. Such future use of this vaccine implies fighting fire with fire, with the risk of seeding additional live viruses into the population.11 As of now, the only other available technology to help curtail transmission of OPV-derived viruses is IPV; but this use of IPV has yet to be assessed in the difficult areas of the world. IPV should at least help (IPV has been sufficient to arrest transmission of all polioviruses in several countries with high levels of hygiene), but only if used at coverage levels which are far higher than currently achieved in several of the poorest countries of the world. The needs of the GPEI might thus become coincident with those of the GAVI Alliance, which has set a target of 90% routine vaccine coverage in lowincome countries by 2010.12 This sharing of interests could prove a powerful lobby for public health. A world in which all children, everywhere, receive all the recommended vaccines could and should be among the legacies of the programme that was started to eradicate poliomyelitis.
*Paul E M Fine, Ulla Kou Griffiths London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK Paul.fi[email protected] We declare that we have no conflict of interest. 1
2
3 4
5
6
7 8
9
10
11 12
WHO. Conclusions and recommendations of the Advisory Committee on Poliomyelitis Eradication, Geneva 11–12 October 2006, part I. Wkly Epidemiol Rec 2006; 81: 453–60. WHO. Conclusions and recommendations of the Advisory Committee on Poliomyelitis Eradication, Geneva 11–12 October 2006, part II. Wkly Epidemiol Rec 2006; 81: 465–68. Grassly NC, Fraser C, Wenger J, et al. New strategies for the elimination of polio from India. Science 2006; 324: 1150–53. Kew OM, Sutter RW, de Gourville EM, Dowdle WR, Pallansch MA. Vaccine-derived polioviruses and the endgame strategy for global polio eradication. Ann Rev Microbiol 2005; 59: 587–635. MacLennan C, Dunn G, Huissoon AP, et al. Failure to clear persistent vaccine-derived neurovirulent poliovirus infection in an immunodeficient man. Lancet 2004; 363: 1509–13. Dowdle W, van der Avoort H, de Gourville E, et al. Containment of polioviruses after eradication and OPV cessation: characterising risks to improve management. Risk Anal 2007; 26: 1449–69. Arita I, Nakane M, Fenner F. Public health: is polio eradication realistic? Science 2006; 312: 852–54. Grassly NC, Wenger J, Durrani S, et al. Protective efficacy of a monovalent oral type 1 poliovirus vaccine: a case control study. Lancet 2007; published online April 12, 2007. DOI:10.1016/S0140-6736(07)60531-5. Thompson KM, Duintjer Tebbens RJ. Eradication versus control for poliomyelitis: an economic analysis. Lancet 2007; published online April 12, 2007. DOI:10.1016/S0140-6736(07)60532-7. Fine PEM, Carneiro IM. Transmissibility and persistence of oral polio vaccine viruses: implications for the global polio eradication initiative. Am J Epidemiol 1999; 150: 1001–21. Fine PEM, Sutter RW, Orenstein WA. Stopping a polio outbreak in the post-eradication era. Dev Biol 2001; 105: 129–47. GAVI. Annex 1: 2007-10 GAVI roadmap. Nov 11, 2006: http://www. gavialliance.org/resources/2007_10_Roadmap_final.pdf (accessed April 4, 2007).
Surveillance of acute flaccid paralysis in India See Comment page 1321 See Articles pages 1356 and 1363
1322
Poliomyelitis eradication requires surveillance for acute flaccid paralysis (AFP), and in all countries children with AFP who are younger than 15 years are investigated for poliovirus in stool. However, collection of two 8-g stool samples 24 h apart and within 14 days of onset of paralysis is not easy. Samples need to be stored below 8°C, documented properly, and tested in an accredited laboratory. Individuals without adequate stool samples are examined by a neurologist with electromyography and nerveconduction and other tests. A national expert committee1 reviews these cases, decides whether any are poliomyelitis, and labels them as compatible poliomyelitis in accordance with WHO’s recommended virological classification scheme.1,2 The occurrence of compatible poliomyelitis suggests a failure of the surveillance system.3
Poliomyelitis eradication in India is a huge challenge. The National Polio Surveillance Project,2 established in India in 1997 to guide public-health experts, has been a successful model for surveillance activities globally. In India, it was hoped that poliomyelitis would be eradicated quickly, but the virus resurged in 2006. It seems that India did everything according to the surveillance rulebook. To avoid missing cases of paralytic poliomyelitis, the prevalence of non-poliomyelitis AFP should be at least 1 per 100 000 in children younger than 15 years. To ensure that we identify the virus, 80% of AFP cases should have adequate stool samples. If these criteria are met and no cases of poliomyelitis are identified for 3 years consecutively, we can conclude fairly certainly that the country is free of poliovirus. However, if the www.thelancet.com Vol 369 April 21, 2007
Global poliomyelitis eradication: status and implications
www.thelancet.com Vol 369 April 21, 2007
wild virus transmission). The cost difference between the posteradication and control scenarios is used to conclude that “we should be willing to invest more than $8000 million to achieve eradication”. The authors conclude that even a policy that included global introduction of inactivated poliomyelitis vaccine (IPV) after the “eradication” of poliomyelitis will, over 20 years, cost less than implementing any of the modelled control strategies. Readers may note that Thompson and Duintjer Tebbens’ use of the phrase “poliomyelitis eradication” for interruption of wild poliovirus transmission is confusing, and exacerbates a semantic problem which has haunted the GPEI since its inception. The termination of wild virus transmission does not guarantee eradication of poliomyelitis disease, considering that OPV viruses are transmissible and are known to revert back to wildtype phenotype.4,10 WHO has recognised this problem and declared that OPV will have to be discontinued if poliomyelitis is to be eradicated.1,2 The essential step of terminating transmission of all OPV-derived viruses remains untested. These two papers provide encouraging insights into the current methods and long-term economics of the GPEI. The demonstration of superior effectiveness of mOPV vaccine adds to the evidence that termination of wild poliovirus transmission is technically feasible, given enough time, continued funding, political stability, and continued political support in the affected areas of the world. The modelled illustration of the financial
Published Online April 12, 2007 DOI:10.1016/S01406736(07)60533-9 See Comment page 1322 See Articles pages 1356 and 1363
The printed journal includes an image merely for illustration Science Photo Library
The Global Polio Eradication Initiative (GPEI) is among the most ambitious programmes ever undertaken by WHO. Begun in 1988, it has made extraordinary progress, reducing the global incidence of poliomyelitis by more than 99%.1,2 Wild poliovirus is now regarded as endemic in only four regions of the world. In Afghanistan and Pakistan, security problems have hampered vaccine delivery. In northern Nigeria, there has been a loss of public confidence in the vaccine, low uptake, and consequent outbreaks which have seeded virus into several other countries. And in the Indian states of Uttar Pradesh and Bihar, the wild virus has proven extraordinarily well entrenched, partly because of low efficacy of conventional trivalent oral poliovirus vaccine (tOPV) in that environment.3 Other problems have arisen that could threaten the feasibility of stopping all poliovirus transmission: the recognition of circulating virus derived from oral vaccine,4 persistent excretion of poliovirus by immunodeficient individuals,5 and difficulties in ensuring containment of all potential sources of reintroduction.6 These difficulties have led to a recommendation that the programme abandons its eradication goal in favour of a control approach.7 Two papers in today’s Lancet provide important perspectives on this debate and on the current stage of the programme. Nicholas Grassly and colleagues analyse recent data from India to compare the effectiveness of a monovalent oral type 1 poliovirus vaccine (mOPV1) with that of tOPV.8 There are problems in inferring absolute vaccine efficacies in such circumstances. But the relative efficacy estimates should be valid, and they indicate that the newer mOPV is more effective than the older tOPV. Let us hope this difference is sufficient to terminate the remaining chains of transmission of type 1 wild poliovirus. Kimberly Thompson and Radboud Duintjer Tebbens use a dynamic model to show that a decrease in immunisation intensity in endemic areas will result in a rapid accumulation of susceptible individuals and many more cases of paralytic poliomyelitis (northern India is used as an example).9 In addition, they argue that both the cumulative number of patients with paralytic poliomyelitis, and the financial costs, that would occur with various control options are higher than with any of four policies suggested for the era after “poliomyelitis eradication” (defined by these authors as interruption of
Coloured transmission electron micrograph of polioviruses
1321
Comment
implications of managing patients with paralytic poliomyelitis and continuing to control poliovirus with supplemental immunisation activities is based on a large number of assumptions, but it supports arguments against abandoning the goal to eradicate wild virus at least. Despite its established efficacy against wild virus, the usefulness of mOPV in combating transmission of vaccine-derived viruses, after the eradication of wild virus, is unclear. Such future use of this vaccine implies fighting fire with fire, with the risk of seeding additional live viruses into the population.11 As of now, the only other available technology to help curtail transmission of OPV-derived viruses is IPV; but this use of IPV has yet to be assessed in the difficult areas of the world. IPV should at least help (IPV has been sufficient to arrest transmission of all polioviruses in several countries with high levels of hygiene), but only if used at coverage levels which are far higher than currently achieved in several of the poorest countries of the world. The needs of the GPEI might thus become coincident with those of the GAVI Alliance, which has set a target of 90% routine vaccine coverage in lowincome countries by 2010.12 This sharing of interests could prove a powerful lobby for public health. A world in which all children, everywhere, receive all the recommended vaccines could and should be among the legacies of the programme that was started to eradicate poliomyelitis.
*Paul E M Fine, Ulla Kou Griffiths London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK Paul.fi[email protected] We declare that we have no conflict of interest. 1
2
3 4
5
6
7 8
9
10
11 12
WHO. Conclusions and recommendations of the Advisory Committee on Poliomyelitis Eradication, Geneva 11–12 October 2006, part I. Wkly Epidemiol Rec 2006; 81: 453–60. WHO. Conclusions and recommendations of the Advisory Committee on Poliomyelitis Eradication, Geneva 11–12 October 2006, part II. Wkly Epidemiol Rec 2006; 81: 465–68. Grassly NC, Fraser C, Wenger J, et al. New strategies for the elimination of polio from India. Science 2006; 324: 1150–53. Kew OM, Sutter RW, de Gourville EM, Dowdle WR, Pallansch MA. Vaccine-derived polioviruses and the endgame strategy for global polio eradication. Ann Rev Microbiol 2005; 59: 587–635. MacLennan C, Dunn G, Huissoon AP, et al. Failure to clear persistent vaccine-derived neurovirulent poliovirus infection in an immunodeficient man. Lancet 2004; 363: 1509–13. Dowdle W, van der Avoort H, de Gourville E, et al. Containment of polioviruses after eradication and OPV cessation: characterising risks to improve management. Risk Anal 2007; 26: 1449–69. Arita I, Nakane M, Fenner F. Public health: is polio eradication realistic? Science 2006; 312: 852–54. Grassly NC, Wenger J, Durrani S, et al. Protective efficacy of a monovalent oral type 1 poliovirus vaccine: a case control study. Lancet 2007; published online April 12, 2007. DOI:10.1016/S0140-6736(07)60531-5. Thompson KM, Duintjer Tebbens RJ. Eradication versus control for poliomyelitis: an economic analysis. Lancet 2007; published online April 12, 2007. DOI:10.1016/S0140-6736(07)60532-7. Fine PEM, Carneiro IM. Transmissibility and persistence of oral polio vaccine viruses: implications for the global polio eradication initiative. Am J Epidemiol 1999; 150: 1001–21. Fine PEM, Sutter RW, Orenstein WA. Stopping a polio outbreak in the post-eradication era. Dev Biol 2001; 105: 129–47. GAVI. Annex 1: 2007-10 GAVI roadmap. Nov 11, 2006: http://www. gavialliance.org/resources/2007_10_Roadmap_final.pdf (accessed April 4, 2007).
Surveillance of acute flaccid paralysis in India See Comment page 1321 See Articles pages 1356 and 1363
1322
Poliomyelitis eradication requires surveillance for acute flaccid paralysis (AFP), and in all countries children with AFP who are younger than 15 years are investigated for poliovirus in stool. However, collection of two 8-g stool samples 24 h apart and within 14 days of onset of paralysis is not easy. Samples need to be stored below 8°C, documented properly, and tested in an accredited laboratory. Individuals without adequate stool samples are examined by a neurologist with electromyography and nerveconduction and other tests. A national expert committee1 reviews these cases, decides whether any are poliomyelitis, and labels them as compatible poliomyelitis in accordance with WHO’s recommended virological classification scheme.1,2 The occurrence of compatible poliomyelitis suggests a failure of the surveillance system.3
Poliomyelitis eradication in India is a huge challenge. The National Polio Surveillance Project,2 established in India in 1997 to guide public-health experts, has been a successful model for surveillance activities globally. In India, it was hoped that poliomyelitis would be eradicated quickly, but the virus resurged in 2006. It seems that India did everything according to the surveillance rulebook. To avoid missing cases of paralytic poliomyelitis, the prevalence of non-poliomyelitis AFP should be at least 1 per 100 000 in children younger than 15 years. To ensure that we identify the virus, 80% of AFP cases should have adequate stool samples. If these criteria are met and no cases of poliomyelitis are identified for 3 years consecutively, we can conclude fairly certainly that the country is free of poliovirus. However, if the www.thelancet.com Vol 369 April 21, 2007