In 1988 the Global Poliomyelitis Eradication Initiative (GPEI) launched a global campaign to eradicate poliovirus by the turn of the century through a programme of mass immunization. Polio has not been eradicated, but the GPEI has achieved remarkable results: in 1988 there were more than 350,000 polio cases in over 125 countries, while in 2014 there were 359 cases of wild polio in ten countries [1–3]. Poliovirus has remained endemic in three countries: Nigeria, Pakistan, and Afghanistan. In the past couple of years polio has spread from endemic countries to cause outbreaks in previously polio free countries: from Nigeria to other countries in West Africa and the Horn of Africa – there were 199 polio cases in Somalia in 2013–14 (the first since 2007); and from Pakistan/Afghanistan to the Middle East – there were 38 cases in Syria and Iraq in 2013–14 (the first since 1999 and 2000 respectively). In May 2014 the WHO declared the renewed spread of poliovirus to be an “extraordinary event” and a “public health emergency of international concern” [4].

Empirical experience demonstrates that eradication is possible. India was until recently the largest endemic reservoir of polio – in 2009 it accounted for almost half of the world’s polio cases – and was considered to be the most difficult challenge for eradication [3, 5]. But India has not had a polio case since 2011 and in 2014 it was declared polio free. This success was the result of two factors. First, new vaccines have been developed against specific strains of the virus. These are particularly effective in areas where sanitation is poor because bacteria that infect the gut interfere with the body’s ability to mount an effective immune response to older vaccines. Second, a concerted effort by the Indian government, in collaboration with the GPEI and other organizations, deployed a large number of workers (more than 250,000 in the state of Uttar Pradesh alone), and paid particular attention to vaccinating children from migratory populations and in dangerous and remote areas [5]. The eradication of polio in India removed any doubts regarding the feasibility of polio eradication. As Bruce Aylward, WHO Assistant Director-General for Polio, pointed out, “Now that India has become polio-free, we have crossed… from our primary barrier being technological or biological feasibility to one of political and societal will” [6].

The technical and biological factors that inhibit polio eradication are well understood. The organisational factors are also understood [7]. The proximate cause of the persistence of polio in some areas and new outbreaks in previously polio free areas is that too few children are vaccinated to stop the spread of poliovirus [8, 9]. Yet the underlying political and societal factors that inhibit the effective implementation of vaccination programmes have attracted little systematic analysis and do not even feature in assessments of risks of outbreaks [10]. There is widespread agreement that civil war is associated with disease in general [11] and barriers to polio eradication in particular [1, 6, 12, 13]. Insurgency diverts resources away from healthcare and public health programmes, disrupts healthcare infrastructure and the organisation of vaccination programmes, and leads to forced migration, which spreads infectious disease and makes populations hard to reach. Reports in newspapers and medical journals have suggested that Islamist insurgents have a particularly negative effect on polio because they deliberately undermine the efficacy of polio immunization campaigns by spreading misinformation that they are a conspiracy to sterilize Muslim populations, which increases the likelihood that parents will refuse vaccinations [8], and carrying out targeted violence and boycotts – often legitimised by these rumours – that reduce the ability and willingness of polio workers to operate in particular areas [12]. Some accounts argue that this reflects Islamists’ adherence to Islam and rejection of non-Islamic influences, which makes them deeply antagonistic towards non-Muslims and the West in particular [14]. More nuanced interpretations suggest that Islamist insurgents’ animus towards eradication programs must be understood in the context of their interaction with domestic political rivals and international actors [15, 16]. Islamic scholars note that there is no religious basis for opposition to polio immunisation and suggest that the primary reason for failure of eradication is the presence of conflict [17].

The first major conflict between Islamists – albeit non-violent Islamists – and polio campaigns occurred in 2003, when the leaders of several northern-Nigerian states banned vaccination programmes following rumours that they were a Western conspiracy to render Muslim children infertile [9, 16, 18]. The boycott lasted a year and was a major setback for polio eradication. It resulted in a global polio outbreak that affected 20 countries, accounted for 80 % of the world’s polio cases at the time, and cost more than US$500 million to control [18]. In Pakistan, resistance to polio campaigns began a few years later: in 2007 militants banned vaccination programmes in the North West Frontier Province due to similar fears [19]. The boycott was accompanied by targeted violence against polio workers – most notably the assassination of the head of the government’s vaccination campaign in Bajaur Agency in 2007. Some observers argue that Islamist insurgents in Pakistan have become increasingly hostile to polio vaccinations in the past couple of years. These accounts stress the CIA’s use of a fake hepatitis immunisation programme to collect DNA from Osama bin Laden’s family members before his assassination in 2011. This seemingly vindicated insurgents’ suspicions that immunization drives are a cover for espionage activities [6, 9, 20]. In addition, the increased use of drone strikes in northwest Pakistan by the United States is said to have amplified Islamist insurgents’ enmity to polio vaccination campaigns because the insurgents suspect that polio workers were carrying out surveillance in order to identify targets for drone strikes [2, 6, 21, 22]. As a result an influential leader of the Pakistani Taliban in North Waziristan banned polio vaccination programmes in areas under his control in summer 2012 [20, 21]. This is said to have led to a steep increase in the number of polio cases in the area [20, 21]. It should be noted, however, that other influential Islamist clerics in Pakistan opposed the ban, issuing Fatwas that encouraging parents to immunize their children against polio and other diseases [23]. In addition, Boko Haram has reportedly carried out several similar attacks on polio workers in northern Nigeria [9, 24]. There have also been alleged attacks in Afghanistan, although these are much less frequent [25]. It should be noted, however, that when the Taliban were in power between 1995 and 2001 they fully supported the GPEI. They continue to support polio campaigns but the diffusion of ideas from Pakistan means that some insurgents are hostile to vaccination programmes and many parents refuse to vaccinate their children [9, 26, 27].

Based on the analysis outlined above we generate three testable hypotheses. The first relates to the widely held conviction that civil war in general increases the likelihood that a country will be affected by polio. It is argued that the violence and disruption of armed conflict undermines the ability of polio workers to carry out mass vaccination programmes, as well as causing a more general public health crisis.

Hypothesis 1: Countries affected by non-Islamist insurgency will have a higher number of polio cases.

The second hypothesis considers the more contentious argument that Islamist insurgency in particular increases the likelihood that a country will be affected by polio. It is argued that Islamist insurgents deliberately undermine the effectiveness of polio immunization campaigns by spreading misinformation and carrying out targeted violence and boycotts.

Hypothesis 2: Countries affected by Islamist insurgency will have a higher number of polio cases.

Thirdly, some observers argue that Islamist insurgents’ animosity towards polio vaccination programmes is the logical result of Islamic theology. If this is the case we would expect the hostility to be more or less constant to reflect the fact that the theological tenets of Islam have not changed over the past decade or so. Alternatively, others stress the role of political dynamics. It seems apparent that some Islamist insurgents have come to realize that interrupting polio campaigns is a useful strategy because it generates international attention for the insurgents and enables them to force concessions from their opponents. Moreover, it is argued that Islamist insurgents’ enmity towards polio vaccination programmes has intensified in recent years in response to the counterinsurgency strategies used against them. The increased use of drone attacks and the CIA’s use of a fake immunisation program in the assassination of Osama bin Laden seemingly vindicated Islamist insurgents’ suspicions that immunization drives are a cover for espionage activities. This is said to have seriously compromised the GPEI’s activities.

Hypothesis 3: The effect of Islamist insurgency on the incidence of polio will be stronger after the assassination of Osama bin Laden in 2011.