Population level impact of an imperfect prophylactic vaccine for herpes simplex virus-2.

BACKGROUND: The continuation of developing Herpes simplex virus type-2 (HSV-2) prophylactic vaccines requires parallel mathematical modeling to quantify the effect on the population of these vaccines. METHODS: Using mathematical modeling we derived 3 summary measures for the population effect of imperfect HSV-2 vaccines as a function of their efficacies in reducing susceptibility (VES), genital shedding (VEP), and infectivity during shedding (VEI). In addition, we studied the population level effect of vaccine intervention using representative vaccine efficacies. RESULTS: A vaccine with limited efficacy of reducing shedding frequency (VEP = 10%) and infectivity (VEI = 0%) would need to reduce susceptibility by 75% (VES = 75%) to substantially reduce the sustainability of HSV-2 infection in a population. No reduction in susceptibility would be required to reach this target in a vaccine that decreased shedding by 75% (VES = 0%, VEP = 75%, VEI = 0%). Mass vaccination using a vaccine with imperfect efficacies (VES = 30%, VEP = 75%, and VEI = 0%) in Kisumu, Kenya, in 2010 would decrease prevalence and incidence in 2020 by 7% and 30%, respectively. For lower prevalence settings, vaccination is predicted to have a lower effect on prevalence. CONCLUSION: A vaccine with substantially high efficacy of reducing HSV-2 shedding frequency would have a desirable effect at the population level. The vaccine's short-term impact in a high prevalence setting in Africa would be a substantial decrease in incidence, whereas its immediate impact on prevalence would be small and would increase slowly over time.