BackgroundThe prevention of tuberculosis (TB) is key for accelerating current, slow declines in TBburden. The 2018 World Health Organization (WHO) guidelines on eligibility forpreventive therapy to treat latent TB infection (LTBI) include: people living with humanimmunodeficiency virus (PLHIV), household contacts of TB patients including children,and those with clinical conditions including silicosis, dialysis, transplantation etc. andother country-specific groups. We aimed to estimate the potential impact of fullimplementation of these guidelines in the WHO South-East Asian (SEA) Region, whichbears the largest burden of TB and LTBI amongst the WHO Regions.MethodsWe developed mathematical models of TB transmission dynamics, calibratedindividually to each of the 11 countries in the Region. We modelled preventive therapyin the absence of other TB interventions. As an alternative comparator, reflectingongoing developments in TB control in the region, we also simulated improvements inthe treatment cascade for active TB, including private sector engagement andintensified case-finding. Relative to both scenarios, for each country in the region weprojected TB cases and deaths averted between 2020 and 2030, by full uptake ofpreventive therapy, defined as comprehensive coverage amongst eligible populationsas per WHO guidelines, and assuming outcomes consistent with clinical trials. We alsoperformed sensitivity analysis to illustrate impact under less-than-optimal conditions.ResultsAt the regional level, full uptake of preventive therapy amongst identified risk groupswould reduce annual incidence rates in 2030 by 8.30% (95% CrI 6.48 – 10.83) relativeto 2015, in the absence of any additional interventions. If implemented against abackdrop of improved TB treatment cascades, preventive therapy would achieve anincremental 6.93 percentage points (95% CrI 5.81 – 8.51) of reduction in annualincidence rates, compared to 2015. At the regional level, the numbers of individualswith latent TB infection that need to be treated to avert 1 TB case is 64 (95% CrI 55 -74). Sensitivity analysis illustrates that results for impact are roughly proportional to‘effective coverage’ (the product of actual coverage and effectiveness of the regimen).ConclusionsFull implementation of WHO guidelines is important for ending TB in the SEA Region.Although future strategies will need to be expanded to the population level, to achievelarge declines in TB incidence, the uptake of current tools can offer a valuable step inthis direction.