Background Economic losses due to herpes simplex infections in low- and middle-income countries (LMICs) are unknown. We estimated economic and quality-of-life losses due to genital herpes in 2019, in 90 LMICs, and from 2020 to 2030 in 45 countries in the World Health Organization (WHO) Africa. We additionally estimated economic losses due to human immunodeficiency virus (HIV) attributable to herpes simplex virus type 2 (HSV-2) infections. Methods and findings We estimated genital herpes-related spending on treatment, wage losses due to absenteeism, and reductions in quality of life, for individuals aged 15 to 49 years, living with genital herpes. Had HSV-2 had contributed to the transmission of HIV, we estimated the share of antiretroviral treatment costs and HIV-related wage losses in 2019 that can be attributed to incident and prevalent HSV-2 infections in 2018. For the former, we used estimates of HSV-2 incidence and prevalence from the global burden of disease (GBD) study. For the latter, we calculated population attributable fractions (PAFs), using the classic (Levin’s) epidemiological formula for polytomous exposures, with relative risks (RRs) reported in literature. To extend estimates from 2020 to 2030, we modeled the transmission of HSV-2 in 45 African countries using a deterministic compartmental mathematical model, structured by age, sex, and sexual activity, which was fitted to seroprevalence gathered from a systematic review and meta-regression analysis. In the 90 LMICs, genital herpes contributed to US$813.5 million in treatment and productivity losses in 2019 (range: US$674.4 to US$952.2 million). Given observed care-seeking and absenteeism, losses are in the range of US$29.0 billion (US$25.6 billion to US$34.5 billion). Quality-of-life losses in the amount of 61.7 million quality-adjusted life years (QALYs) are also possible (50.4 million to 74.2 million). The mean annual cost of treatment and wage losses per infection is US$183.00 (95% CI: US$153.60 to US$212.55); the mean annual cost of quality-of-life losses is US$343.27 (95% CI: 272.41 to 414.14). If HSV-2 has fueled the transmission of HIV, then seroprevalent HSV-2 cases in 2018 can account for 33.2% of the incident HIV infections in 2019, with an associated antiretroviral therapy (ART) cost of US$186.3 million (range: US$163.6 to US$209.5 million) and 28.6% of HIV-related wage losses (US$21.9 million; range: US$19.2 to US$27.4 million). In the WHO Africa region, the 3.9 million seroprevalent genital herpes cases from 2020 to 2030 contributed to US$700.2 million in treatment and productivity losses. Additionally, quality-of-life losses in the range of 88 million to 871 million QALYs are also possible. If HSV-2 has contributed to the transmission of HIV, then in 2020, the PAF of HIV due to prevalent HSV-2 will be 32.8% (95% CI: 26.7% to 29.9%) and due to incident infections will be 4.2% (95% CI: 2.6% to 3.4%). The PAF due to prevalent infections will decline to 31.0% by 2030 and incident infections to 3.6%. Though we have accounted for the uncertainty in the epidemiological and economic parameter values via the sensitivity analysis, our estimates still undervalue losses due to limiting to the 15- to 49-year-old population. Conclusions Economic losses due to genital herpes in LMICs can be large, especially when considering the lifelong nature of the disease. Quality-of-life losses outweigh spending on treatment and reductions in productivity. If HSV-2 has contributed to the spread of HIV in LMICs, then nearly one third of antiretroviral costs and HIV-related wage losses can be attributed to HSV-2. Given the magnitude of the combined losses, a vaccine against HSV-2 must be a global priority. In a modelling study, Dr Sachin Silva and colleagues estimate the economic burden of genital herpes and HIV attributable to herpes simplex virus type-2 infections in 90 low and middle income countries. Author summary Why was this study done? ▪ Economic losses due to herpes simplex virus type 2 (HSV-2) infections in low- and middle-income countries (LMICs) are unknown. ▪ Quality-of-life losses due to genital herpes in LMICs are also unknown, both in terms of their magnitude and their economic value. ▪ If HSV-2 has indeed fueled the spread of human immunodeficiency virus (HIV), as has been conjectured, then the share of HIV-related spending in LMICs that are attributable to HSV-2 infections are also unknown. What did the researchers do and find? ▪ We estimated direct and indirect economic losses and quality-of-life losses due to genital herpes in individuals between the aged of 15 to 49 living in 90 LMICs in 2019. ▪ We also estimated these costs in 45 countries in the World Health Organization (WHO) Africa region from 2020 to 2030, by constructing a mathematical model of HSV-2 dynamics to predict HSV-2 incidence and prevalence. ▪ We supplemented the 2019 estimates with the share of HIV-related spending in 2019 attributable HSV-2 infections in 2018. ▪ For the 90 LMICs, we found that treatment costs and productivity losses in 2019 are in the range of US$674.4 and US$952.2 million. ▪ Quality-of-life losses are in the range of 50.4 million to 74.2 million quality-adjusted life years (QALYs). ▪ Additionally, seroprevalent HSV-2 cases in 2019 can account for 33.2% of antiretroviral therapy (ART) costs for incident HIV cases and 28.6% of HIV-related wage. What do these findings mean? ▪ Economic losses due to genital herpes can be substantial, especially when considering the lifelong nature of the disease. ▪ The quality-of-life losses due to genital herpes outweigh spending on treatment and reduced productivity (on the order of US$212 billion). ▪ If HSV-2 has indeed contributed to the transmission of HIV, then nearly one third of antiretroviral costs and HIV-related wage losses add to these costs. ▪ Given the magnitude of the above losses in LMICs, a vaccine against HSV-2 should be a global priority.