LAUSR

Background Crimean-Congo haemorrhagic fever virus (CCHFV) is a highly pathogenic virus for which a safe and effective vaccine is not yet available, despite being considered a priority emerging pathogen. Understanding transmission patterns and the use of potential effective vaccines are central elements of the future plan against this infection. Methods We design a modelling approach to explain viral transmission amongst livestock, and spillover transmission into humans. While doing this we assess the value of environmental drivers as proxy indicators of vector activity and systematically select the best model using deviance information criteria. Finally, we assess the impact of vaccination by simulating campaigns targeted to humans or livestock, and to high-risk subpopulations (i.e, farmers). We use real-world human and animal data from a CCHFV endemic area in Afghanistan (Herat) to calibrate our models. Findings Our model selection analysis shows that saturation deficit is the indicator that better explains tick activity trends in Herat and that recent increments in reported CCHFV cases in this area are more likely explained by increased surveillance capacity instead of changes in the background transmission dynamics. Modelling suggests that clinical cases only represent 31% (95% CrI 28%-33%) of total infections in this area. A vaccination campaign in humans would result in a much larger impact than livestock vaccination (266 vs 31 clinical cases averted respectively) and a more efficient option calculated as courses per case averted (35 vs 431 respectively. Targeted vaccination to farmers while impactful, also results in 19 courses per case averted (95% CrI 7-62) compared to targeting the general population (35 95% CrI 16-107) Interpretation CCHFV is endemic in Herat, and transmission cycles are well predicted by environmental drivers like saturation deficit. Vaccinating animals could result in less impactful and less efficient campaigns, and importantly targeted interventions to high-risk groups like farmers can offer a much more efficient approach to vaccine roll-out.