Comparing methods of assessing dog rabies vaccination coverage in rural and urban communities in Tanzania

Rabies can be eliminated by achieving comprehensive coverage of 70% of domestic dogs during annual mass vaccination campaigns. Estimates of vaccination coverage are, therefore, required to evaluate and manage mass dog vaccination programs; however, there is no specific guidance for the most accurate and efficient methods for estimating coverage in different settings. Here, we compare post-vaccination transects, school-based surveys, and household surveys across 28 districts in southeast Tanzania and Pemba island covering rural, urban, coastal and inland settings, and a range of different livelihoods and religious backgrounds. These approaches were explored in detail in a single district in northwest Tanzania (Serengeti), where their performance was compared with a complete dog population census that also recorded dog vaccination status. Post-vaccination transects involved counting marked (vaccinated) and unmarked (unvaccinated) dogs immediately after campaigns in 2,155 villages (24,721 dogs counted). School-based surveys were administered to 8,587 primary school pupils each representing a unique household, in 119 randomly selected schools approximately 2 months after campaigns. Household surveys were conducted in 160 randomly selected villages (4,488 households) in July/August 2011. Costs to implement these coverage assessments were $12.01,$66.12, and $155.70 per village for post-vaccination transects, school-based, and household surveys, respectively. Simulations were performed to assess the effect of sampling on the precision of coverage estimation. The sampling effort required to obtain reasonably precise estimates of coverage from household surveys is generally very high and probably prohibitively expensive for routine monitoring across large areas, particularly in communities with high human to dog ratios. School-based surveys partially overcame sampling constraints, however, were also costly to obtain reasonably precise estimates of coverage. Post-vaccination transects provided precise and timely estimates of community-level coverage that could be used to troubleshoot the performance of campaigns across large areas. However, transects typically overestimated coverage by around 10%, which therefore needs consideration when evaluating the impacts of campaigns. We discuss the advantages and disadvantages of these different methods and make recommendations for how vaccination campaigns can be better monitored and managed at different stages of rabies control and elimination programs

Progress towards rabies elimination from Pemba Island, Southern Tanzania

ObjectiveUsing active surveillance approaches to investigate the transmissiondynamics of rabies on Pemba Island and across Southern Tanzania,whilst a large-scale dog vaccination program was underway1, to gaina greater understanding of the dynamics of infection as the disease isdriven towards elimination.IntroductionRabies is endemic in Tanzania and has circulated on Pemba Islandsince the late 1990s. In 2010, an elimination programme was initiatedin Southern Tanzania to demonstrate that human rabies deathscan be eliminated through mass dog vaccinations. We used activesurveillance approaches2to investigate the dynamics of rabies acrossthe area where this programme was implemented.MethodsGovernment census data and post-vaccination transects were usedto estimate the dog population and coverages achieved by vaccinationcampaigns. Routine surveillance of animal bite injuries using a mobilephone-based surveillance system3and active contact tracing wereused to identify animal rabies cases and human exposures. Epidemictrees were constructed using spatiotemporal distances between casesand used to estimate the effective reproduction number (Re). Weexamined factors affecting rabies incidence and transmission usinggeneralized linear mixed models.ResultsWe estimated a small dog population of 4095 and low dog:humanratio on Pemba (1:105). Overall island-wide vaccination coverageincreased from 16.8% in 2011 to 68.2% in 2014. We found a further48 human exposures (343%), who either were not reported or did notobtain post exposure prophylaxes (PEP). Routine surveillance wasfound to detect less than 10% (~8.75%). There was a rapid declinein cases detected on Pemba, from 42 before mass dog vaccinationswere implemented in 2011, to 2 cases in 2014 (Figures 1). Since May2014, no rabies cases have been detected. Similarly, Redeclined from1.02 to 0 and a significant relationship was found with rabies casesdecreasing with increasing vaccination coverage (p= 0.013, Figure 2).Across seven other districts on the Tanzanian mainland we alsoobserved major declines in rabies cases with very few cases of rabiesin dogs detected in 2016 (Figure 3).ConclusionsWe conclude that rabies has been eliminated from domestic dogpopulations on Pemba over the five years since vaccination campaignshave been implemented. Continued surveillance and investigationsof any bite incidents are therefore needed to ensure any subsequentincursions are controlled and freedom from rabies is maintained.On the Tanzanian mainland, it has taken longer to control rabies,however trajectories look promising with several districts close toeliminating the disease. However, detection of some wildlife casesin the last 12 months in these districts indicates the need to furtherinvestigate remaining foci and the role of wildlife in maintenance