Key Issues in the Persistence of Poliomyelitis in Nigeria: A Case-Control Study

"...[D]espite huge investments in communication, refusals and unawareness of vaccine availability or importance still dominate as reasons for failing to immunise children who develop poliomyelitis."

Noting that the completion of poliomyelitis eradication is "a global emergency for public health", this study aimed to quantitatively analyse the key factors sustaining transmission of poliomyelitis in Nigeria and to calculate clinical efficacy estimates for the oral poliovirus vaccines (OPV) currently in use. Researchers used acute flaccid paralysis (AFP) surveillance data from Nigeria collected between January 2001 and December 2012 to estimate the clinical efficacies of all 4 OPVs in use and combined this with vaccination coverage to estimate the effect of the introduction of monovalent (mOPV) and bivalent (bOPV) on vaccine-induced serotype-specific population immunity. One component of the research involved considering the reasons for the high vaccine refusal rate along with risk factors for a given local government area (LGA) reporting a case.

As detailed here, in Nigeria, poliomyelitis cases doubled between 2011 and 2012, with sustained transmission of all 3 serotypes in 2012 (a year in which more than 50% of the world's cases occurred). The question this study seeks to explore is: why has Nigeria has been experiencing continued high caseloads despite having achieved "record successes in vaccine coverage and political and community engagement"? For example, in 2012, the 2011 Nigeria Emergency Action Plan was refined to further involve key political and traditional leaders, and hundreds of volunteer community mobilisers were charged with reaching every child in Nigeria to administer the OPV. This 2012 plan built on lessons learned in previous years, aiming to "integrate almost real-time feedback from teams on the ground with the highest level of governance to ensure chronically missed children are protected and supplies reach the most vulnerable children."

Communication-related findings related to the fact that advances in immunity were driven by the more effective mOPV and bOPV formulations introduced in 2005 and 2009, respectively, along with an increase in the overall number of doses reported, include: "Caregiver refusal of vaccination became less common as a reason for children with poliomyelitis to miss OPV doses, although rates remained high (21·0% for routine and 50·9% for supplementary immunisation activities in 2012; figure 3 [see page e94]). The main reported reasons for missing routine OPV doses in 2012 were an ignorance of vaccine importance or vaccine availability (32·1% and 29·6% of cases, respectively). In 2012, 21 (24·1%) of the 87 confirmed cases with a known vaccination history listed in the follow-up database had received no OPV....A nomadic lifestyle was not significantly associated with a failure to vaccinate..."

Overall, in addition to the communication issues (refusals and unawareness) described above, the study shows that the persistence of poliovirus in northern Nigeria is driven by the fact that: (i)"vaccine efficacy seems to be lower in northern states compared with southern states" and (ii) "coverage and population immunity remain too low to interrupt wild poliovirus transmission".

One section of the discussion section of the paper focuses on the principal reason for children with poliomyelitis to miss routine immunisations, which researchers found to be tied to "an ignorance of its importance, reaffirming the recommendations made by the Independent Monitoring Board of the Global Polio Eradication Initiative that promotion of demand generation is vital to eradication." The recommendation offered here is that "[t]he primary source of information on health issues strongly affected an individual's probability of receiving OPV and so should be a priority for eradication programmes." The researchers point to a "strong link between receiving OPV and obtaining health education via town announcers", which they say has been previously recognised and used as a way of promoting a positive message about vaccination. Also, in Pakistan and Afghanistan, targeted social mobilisation activities aimed at improving community perceptions reportedly reduced cases by 66% between 2011 and 2012 (citations are included in the report.)

In conclusion: "Although high refusal rates, low OPV campaign awareness, and heterogeneous population immunity continued to support poliomyelitis transmission in Nigeria at the end of 2012, overall population immunity had improved due to new OPV formulations and improvements in programme delivery."