What kind of impact would a herpes vaccine have on the general population? A recently completed study uses mathematical modeling to gauge the population level effect of a prophylactic vaccine for HSV-2.
Researchers examined the effect of a HSV-2 vaccine on susceptibility, frequency of shedding and infectivity during shedding. While similar studies used the United States as a representative sample, researchers in this study used Kisumu, Kenya as their representative setting. This setting allowed for the estimation of the population level effect in a hyperendemic* HIV and HSV-2 epidemic area.
Researchers used a compartmental model to assess HSV-2 transmission in various populations with the hypothetical vaccination present. This compartmental model “stratifie[d] the population into compartments according to vaccination status (vaccinated or unvaccinated), sexual risk group, and stage of HSV-2 infection …”1
Even with an imperfect vaccine researchers found a 3% reduction of HSV-2 prevalence by the year 2020 if an adolescent vaccination intervention was instituted. Incidence which is the number of new cases of a specific disease during a certain period of time would decrease by 21% in this scenario. Overall, a total of 3842 infections would be prevented.
An examination of the effects of vaccinating all people between the ages of 15 to 49 susceptible to HSV-2 revealed increased reductions of HSV-2 prevalence, incidence and incidence rate. By 2020, a mass population vaccination would yield a 7% reduction in HSV-2 prevalence and a 30% reduction in incidence. In this scenario, prevention of 8430 infections would occur.
In developing these models, researchers emphasize the importance of studying viral shedding in conjunction with vaccination studies: Vaccines with no effect on shedding but some effect on acquisition are likely to be ineffective, so it is imperative vaccine studies examine the effects not only on acquisition but viral shedding as well.
*Hyperendemic-has a high and continued incidence
1. Alsallaq RA, Schiffer JT, Longini IM Jr, Wald A, Corey L, Abu-Raddad LJ. Population level impact of an imperfect prophylactic vaccine for herpes simplex virus-2. Sex Transm Dis. 2010 May;37(5):290-7.