The population impact of herpes simplex virus type 2 (HSV-2) vaccination on the incidence of HSV-2, HIV and genital ulcer disease in South Africa: a mathematical modelling study

Background: Evidence suggests HSV-2 infection increases HIV acquisition risk and HIV/HSV-2 coinfection increases transmission risk of both infections. We analysed the potential impact of HSV-2 vaccination in South Africa, a high HIV/HSV-2 prevalence setting. Methods: We adapted a dynamic HIV transmission model for South Africa to incorporate HSV-2, including synergistic effects with HIV, to evaluate the impact of: (i) cohort vaccination of 9-year-olds with a prophylactic vaccine that reduces HSV-2 susceptibility; (ii) vaccination of symptomatically HSV-2-infected individuals with a therapeutic vaccine that reduces HSV shedding. Findings: An 80% efficacious prophylactic vaccine offering lifetime protection with 80% uptake could reduce HSV-2 and HIV incidence by 84.1% (95% Credibility Interval: 81.2–86.0) and 65.4% (56.5–71.6) after 40 years, respectively. This reduces to 57.4% (53.6–60.7) and 42.1% (34.1–48.1) if efficacy is 50%, 56.1% (53.4–58.3) and 41.5% (34.2–46.9) if uptake is 40%, and 29.4% (26.0–31.9) and 24.4% (19.0–28.7) if protection lasts 10 years. An 80% efficacious therapeutic vaccine offering lifetime protection with 40% coverage among symptomatic individuals could reduce HSV-2 and HIV incidence by 29.6% (21.8–40.9) and 26.4% (18.5–23.2) after 40 years, respectively. This reduces to 18.8% (13.7–26.4) and 16.9% (11.7–25.3) if efficacy is 50%, 9.7% (7.0–14.0) and 8.6% (5.8–13.4) if coverage is 20%, and 5.4% (3.8–8.0) and 5.5% (3.7–8.6) if protection lasts 2 years. Interpretation: Prophylactic and therapeutic vaccines offer promising approaches for reducing HSV-2 burden and could have important impact on HIV in South Africa and other high prevalence settings. Funding: WHO, NIAID.