Response to “A better way forward for rabies control in India?"
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Dr Andrea Britton, Dr Helen Byrnes, and Dr Thinlay Bhutia comment on a GARC newsletter article from the last issue which described the Tamil Nadu rabies intervention and cost-effectiveness modelling study by Fitzpatrick et al. in PNAS December 2016.
“A quantitative modelling of the role of dog population vaccination using local India data is valuable and demonstrated the higher cost-effectiveness of a more comprehensive dog vaccination strategy that included vaccination of stray dogs (in comparison to the current baseline strategy based on providing PEP and vaccination of 34% of the owned dog population). The paper will be a useful resource for policy-makers planning rabies in elimination in India, however, we’d like to draw attention to some elements of the paper.
Firstly, while the conclusions of the study were clearly reflected in the GARC newsletter, we are concerned that some ambiguities in the paper’s abstract may have led to misperceptions about the results. It would be most unfortunate if the sentence "We found that highly feasible strategies focused on stray dogs, vaccinating as few as 7% of dogs annually, could very cost-effectively reduce human rabies deaths by 70% within 5 y, and a modest expansion to vaccinating 13% of stray dogs could cost-effectively reduce human rabies by almost 90%” was taken to mean that only 13% of dogs need to be vaccinated. Infact the paper argues that vaccination of an additional 7-13% of stray dogs, over and above the vaccinated owned dogs (34%) could effectively reduce human rabies by almost 90%. Some news reports of the study have already demonstrated confusion between the recommendations from the model for vaccination levels across the State and across the whole of India.
Secondly, it is important to note that the conclusions are based on modelling, and the assumptions contained in the model will affect the outcomes. Some of the assumptions need further examination. For example;
- The authors provide no comment on the methodology and consequent reliability of the 19th Livestock Census – 2012 used to estimate the stray dog population.
- The model assumes a closed population with perfect protection and lifelong immunity from rabies after one vaccination dose, with an assumed dog lifespan of 3 years. Roaming dog populations are not closed, particularly if there is high population turnover, however following the implementation of dog population management programs in Sikkim India, and in remote indigenous communities in Australia, the lifespan of roaming dogs is found to be often greater than three years.
- The model assumes that 4-person teams vaccinate a maximum of 120 dogs daily. In the 2016 state-wide vaccination program in Sikkim, 2-person teams vaccinated between 91-235 dogs per day depending on population density. This difference in dog catching and rabies vaccination numbers between Tamil Nadu and Sikkim has significant cost implications and is worth exploring further.
The assumptions of a model are critical to interpreting its findings. We welcome this analysis of rabies control in Tamil Nadu and suggest that recently-published data from the state of Sikkim could further improve model parameterisation. It is vital in India that policy makers do not reduce investments in relation to current levels of canine rabies vaccination and other interventions recommended in the global framework for dog-mediated human rabies elimination, but increase investments to reach additional stray dog vaccination targets.”
Dr Andrea Britton and Dr Helen Byrnes are Directors of Vets Beyond Borders, Australia and Dr Thinlay Bhutia, works with the SARAH program in Sikkim, India.