THE LAST MILE IN GLOBAL POLIOMYELITIS ERADICATION

Tuesday, 4th of October 2011

The Lancet, Volume 378, Issue 9791, Pages 549 - 552, 13 August 2011

Published Online: 09 June 2011

Best viewed at http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(11)60744-7/fulltext

The last mile in global poliomyelitis eradication

Original Text

Zulfiqar A Bhutta a

Before the development of the inactivated poliovirus vaccine (IPV) in 1955, poliomyelitis paralysed and killed up to half a million people every year. The introduction of the IPV in the USA led to a dramatic reduction in poliomyelitis transmission and cases, from an average 20 000 cases per year in the 1950s to less than 1000 cases by the 1960s.1 With the development of the oral poliovirus vaccine (OPV) and the strategy to give two doses of trivalent OPV to all children younger than 5 years in mass vaccination campaigns, transmission was stopped in the USA by 1979.2 Similar campaigns were launched in many developing countries, notably in Latin America, following an initiative by the Pan American Health Organization to eradicate poliomyelitis in the Americas by 1990. In 1988, the World Health Assembly (WHA), with support and funding from Rotary International, unanimously launched a global goal to eradicate poliomyelitis by 2000.3 Since then the achievements of the Global Poliomyelitis Eradication Initiative, one of the largest global public health programmes, have been remarkable. From a situation in which poliomyelitis was endemic in 125 countries on five continents, paralysing 350 000 children annually, there has been a 99% decrease in the global incidence of the disease,4 with only 20 countries with endemic disease in 2000. One of the three serotypes of wild poliovirus (serotype 2) has been eradicated since 1999.

Despite these impressive initial gains, the last phase of poliomyelitis eradication has been difficult, with uneven progress over the past 5 years (figure). In recognising these trends, WHA called for a new plan to complete the eradication effort and the global eradication strategy was revitalised at its 61st session in May, 2008. Over the past 2 years, transmission of indigenous wild poliovirus types 1 and 3 has continued in geographically limited areas in four countries (Nigeria, India, Pakistan, and Afghanistan), and has also affected countries with low coverage of routine immunisation and weak health systems in central Africa and the horn of Africa.6 Nigeria and India have made enormous gains in the control of poliomyelitis throughout the past year with a more than 90% reduction in cases. Even war-torn Afghanistan has shown a 34% reduction in cases, but Pakistan remains a huge challenge. Inefficiencies within the eradication programme in Pakistan, compounded by recent floods and a smouldering conflict in the north, were associated with a 62% increase in cases, with 144 confirmed children with poliomyelitis in 2010 and over 35 cases in the first quarter of 2011.7 In view of these concerns about slow progress in global eradication, WHO's Director-General established an Independent Monitoring Board of the Global Poliomyelitis Eradication Initiative in 2010. The Board's most recent report (April, 2011)5 presented a mixed picture, noting impressive gains in some parts of the world and residual challenges in others. The overarching theme of the Board and global public health community is continued emphasis on implementation and close monitoring of the current eradication strategy. The Board has rightly underscored several crucial success factors, such as political support, vaccine efficiency, sound surveillance strategies, operational innovations, and demand creation. However, there is a funding gap of US$665 million from the $1·21 billion required for 2010—12.

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Global trends in number of cases of poliomyelitis

Adapted from Independent Monitoring Board of the Global Polio Eradication Initiative.5

Notwithstanding the importance of continued focus on staying the course, there are other crucial but neglected issues. Remarkably little public debate about these issues has taken place nationally or globally. Broadly, the issues can be summarised as three challenges which must be met if poliomyelitis is to be eradicated. First, there is a knowledge gap that must be confronted and addressed. Despite the remarkable success of the OPV over time, the current product might not be ideal for the last phase of eradication and for clearing residual pockets of disease. Although impressive seroconversion rates have been reported from many parts of the world,8, 9 the trivalent or monovalent vaccines are not uniformly effective. Of the 144 patients with confirmed poliomyelitis in Pakistan in 2010, 43% had received four or more doses of OPV, suggesting that the vaccine might not be effective in a subset of the population.10 Poor seroconversion after vaccine administration in undernourished children has been reported (Petri W, University of Virginia, VA, USA, personal communication; and my own observations). Although the research needed to develop more effective vaccines and vaccination strategies should not detract from the current global initiative, we need a greater understanding of the vaccine's effectiveness, or lack thereof, in population subsets.

Mucosal immunity induced by the current OPV is imperfect and potentially allows immunised individuals to participate in asymptomatic wild-type poliovirus transmission in settings with efficient faecal-oral transmission of infection. 0·74% of fully vaccinated and asymptomatic children in India continued to excrete wild poliovirus types 1 and 3, and two-thirds of these children had received six or more OPV doses, which is a concern.11 The most recent outbreak of infection, involving 315 cases of type-2 circulating vaccine-derived poliovirus (cVDPV2, >1% divergent from Sabin 2) occurred in Nigeria between July, 2005 and June, 2010, when 23 of 34 supplementary immunisation campaigns used monovalent or bivalent OPV lacking Sabin 2.12 The increased use of serotypes 1 and 3 monovalent OPV might have resulted in improvements in vaccine-induced population immunity against these serotypes, and in declines in immunity to cVDPV2.13 These findings are indicative of the need for control scenarios to take into account the possibility of dealing with virulent vaccine-derived polioviruses at scale, and the potential benefit of including IPV in the eradication strategy in such countries.14 The successful development and use of bivalent OPV is a welcome step for improvement of eradication strategies,15 as are trials of fractionated doses of IPV16 which could make the product more affordable, either singly or in combination with OPV.

Second, are the current strategies for eradication satisfactory? The usual approaches to eradication for the remaining pockets of endemic disease are large-scale national and subnational immunisation days. The evolving epidemiology of poliomyelitis also suggests that population immunity-thresholds needed to interrupt wild-poliovirus transmission differ around the world, and are substantially higher in northern India and parts of Pakistan than in Africa and elsewhere. Although this understanding has led to the systematic development of targeted district-specific and population-specific strategies, and capacity to address heterogeneity in OPV coverage, the mainstay is still a largely vertical strategy for eradication, often distinct from routine expanded programmes for immunisation services. Whereas this separation has not been an issue in countries with strong programmes, in countries where these services are dysfunctional, serious issues of vaccination-programme mismatch are created, affecting overall control.17 For example, of the 144 patients with poliomyelitis in Pakistan in 2010, 67% were younger than 2 years and 68% had not received any routine immunisation.10 This finding is indicative of the difficulty of trying to eradicate poliomyelitis through a parallel programme delinked from routine expanded services. This approach is possible, but is fraught with the risk of failure. Integration of eradication strategies and routine immunisation services should be possible, because the inequity of resources, manpower, and surveillance systems for both programmes is a serious limitation for control and eradication of the disease. The risk of reintroduction of poliomyelitis into countries now free from the disease is compounded by poor overall immunisation rates, as in parts of Africa, Pakistan, and Tajikistan. Programme managers vehemently deny the lack of integration between poliomyelitis and expanded programmes for immunisation, but the reality on the ground suggests otherwise. Huge differentials exist between the two programmes for overall support services, financial resources, staff incentives for performance, and surveillance methods. WHO's recent decision to separate the poliomyelitis programme from the mainstream vaccination cluster also sends the wrong message when there is much need to focus on integration rather than fragmentation.

Finally, community engagement and creation of grass-roots support for poliomyelitis eradication is key, and related to the issues already mentioned. Without adequate demand-creation, and understanding barriers and addressing them systematically, approaching populations in the same way as before is naive. In many parts of urban and rural Pakistan (and possibly elsewhere), the only vaccination service that people are aware of and access is the poliomyelitis programme; and with home delivery of OPV, incentivising people to seek routine immunisations in expanded programmes is a challenge. The recognition that a substantial proportion of residual disease (both from wild viruses and cVDPV) is in children who have received multiple doses of OPV is a source of disquiet from communities. In these circumstances innovative strategies that couple OPV and IPV could be a way forward.

All these issues should not detract from the importance of staying on track in the final phase of the global strategy for poliomyelitis eradication. However, without adequately addressing some of the real barriers to eradication and creation of innovative solutions to tackle emerging issues, the risk of failure is high. Although we agree with the sentiments of Stephen Cochi, from the US Centers for Disease Control and Prevention, that “to stop now would be snatching defeat from the jaws of victory,”18 victory is by no means assured. All resources and collective wisdom should be combined to ensure that the last mile in the race to eradicate poliomyelitis is the very last mile that we ever run in the quest to relegate poliomyelitis to the corridors of history.

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My institution has grants from WHO to measure poliomyelitis seroprevalence in Pakistan and to assess nutrition interventions and poliomyelitis response. I am also a member of WHO's Strategic Advisory Committee for Vaccines, and the Regional Techincal Advisory Group for Polio for WHO Regional Office for the Eastern Medditerranean. The views in this Comment are my own.

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a Division of Women and Child Health, Aga Khan University, Karachi 74800, Pakistan