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ERADICATING POLIO: PERSISTING CHALLENGES BEYOND ENDEMIC COUNTRIES

Thursday, 12th of January 2012

Expert Review of Vaccines

December 2011, Vol. 10, No. 12, Pages 1635-1636 , DOI 10.1586/erv.11.156

(doi:10.1586/erv.11.156)

Eradicating polio: persisting challenges beyond endemic countries

Heidi J Larson^† & Pauline Paterson

† Author for correspondence

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In the second decade following the aspired to eradication date, persisting polio cases continue to challenge the Global Polio Eradication Initiative. The problem is that the remaining cases do not persist in the same place, but continue to surprise with outbreaks in previously ‘polio-free’ nonendemic locations. New strategies are needed to better anticipate where the next cases may appear, while better information is needed on the reasons why children continue to be missed and not vaccinated in locations where we do know that the virus is circulating.

Tackling polio in the last of the endemic countries – Pakistan, Afghanistan, Nigeria and India – has been a continuing priority for the Global Polio Eradication Initiative. And, so far, India has been the good news story with only one case in January 2011.

Pakistan has been the not-so-good news story – especially with Pakistani strains of the polio virus spilling over its northern border and causing an outbreak in China, which had been polio-free since 1999. As of 26 October 2011, there were 18 cases confirmed in China [101]. In Pakistan, continuing security threats, massive floods that have displaced millions of people and health worker complaints and boycotts over late and inadequate pay are among the various challenges that face the polio eradication effort [1,102]. The President of Pakistan launched a 2011 Emergency Action Plan [103] at the start of the year but, in addition to the logistical obstacles, pockets of public distrust persist; 14,645 children were not vaccinated in the Balochistan Province in the July immunization rounds due to families refusing the vaccine, while 22,000 families rejected the vaccine in Karachi [104]. What is now needed is concomitant social will to match the high-level political will to eradicate polio.

Nigeria and Afghanistan, the two other polio-endemic countries, each had more cases of wild polio virus by September in 2011 than in all of 2010; this is after Nigeria had started to show a promising turning point in 2009 [2]. While security concerns persist in Nigeria – amplified by the August bombing of UN headquarters in Abuja – a quarter of the children not vaccinated in the July 2011 immunization campaign were due to refusals – with greater than 80% of refusals in the northern States of Kano, Sokoto and Jigawa [104]. As in Pakistan, high-level political commitment in Nigeria is not matched with societal support among some subpopulations.

While keeping the pressure on eradicating polio in the remaining endemic countries is crucial, the Independent Monitoring Board of the Global Polio Eradication Initiative raised alarm in their July 2011 meeting report [105] regarding the dramatically increasing number of polio cases in nonendemic countries – particularly those with re-established transmission (persisting poliovirus transmission for more than 12 months after an importation of the virus) – namely Chad, Democratic Republic of Congo, Angola and Sudan (suspected). Chad is the most concerning as the country with the highest number of cases among nonendemic countries. In the short time between the Independent Monitoring Board report in July and the 26 October 2011 global update report [101], the number of polio cases in Chad rose from 80 to 114, the numbers in DRC have risen from 59 to 84; and Cote d’Ivoire had a new outbreak of 35 cases of wild poliovirus (WPV) type 3 after having had no cases of WPV type 3 since 1999 [106]; Côte d’Ivoire had imported WPV type 1 in 2008–2009. It is important to recognize that these numbers are only counting paralytic cases: for every one case of acute flaccid paralysis caused by polio, there are between 200 and 1000 others (depending on the virus type) who are infected, but nonparalytic, and still shedding and transmitting the polio virus.

The list of nonendemic countries includes 14 additional countries with circulating imported polio virus, of which nine constitute what has now become defined as the ‘WPV importation belt’ across Africa, with viruses primarily imported from Nigeria. Others on the list include Nepal, Russia, Kazakhstan, Tajikistan and Turkmenistan, where the polio viruses originally came from India, albeit transiting through other countries.

In short, by the end of September 2011, 63% of the world’s remaining polio cases were in nonendemic countries. And one year earlier, as many as 82% of the global polio cases were in nonendemic countries.

The issue of nonvaccinated ‘missed children’

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In the 2010 Expert Review of Vaccines editorial on polio eradication by Wassilak and Orenstein, they pointed to the two critical reasons for continuing WPV transmission: failure to vaccinate and vaccine failure [2]. On the issue of addressing vaccine failure, which was of particular concern in India, there has been significant progress. On the issue of failure to vaccinate, the problems persist.

As in Pakistan and Nigeria, nonvaccinated or ‘missed children’ are an issue in tackling polio in nonendemic countries. In independent monitoring reports, information is collected on the reasons why children are missed in supplementary immunization activities. In Côte d’Ivoire, for example, of 638 children missed during the June immunization rounds, 163 were because no immunization team visited the house, 357 were because children were ‘absent’ when the house was visited, 30 households refused vaccination and 88 were missed for ‘other reasons’. While such information is valuable, at this stage of the eradication effort, where every child counts more than ever, ‘other’ is not enough data to inform a strategy to reach every last child. Even the coding of a child as ‘absent’ is ambiguous and can suggest a silent refusal to vaccinate by the household. In Kenya, for instance, the monitoring report says that 81% of the parents were aware of the vaccination campaign, yet the same report says that 911 children were absent when the houses were visited by the vaccination team, 214 were not vaccinated for ‘other’ reasons and 13 refused. It is clear that such a high amount of awareness about the campaigns does not necessarily imply acceptance. In Nepal, the independent report from the March 2011 immunization rounds indicates that 97% of the parents were aware in advance of the campaign dates, yet 585 children were ‘absent’, there were 166 outright refusals and 1043 were not vaccinated for ‘other reasons’. As another example, in DRC over a quarter of a million (264,374) children who were reported as not having been vaccinated have the reason classified as ‘other’. ‘Other’ is just not good enough information at this stage of the polio eradication effort if it is effectively going to be able to reach those children [104].

If polio eradication is going to be achieved, it is time for another shift in strategy [3]. The reasons why children are not getting vaccinated need more specific understanding. The level of detail needed now would not have been appropriate nor affordable at earlier stages of the eradication effort. However, it is now urgent.

Financial & competing interests disclosure

H Larson’s research on vaccines is funded by the Bill & Melinda Gates Foundation. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.