While an early study of a recombinant gD2 vaccine adjuvanted

with alum reduced the rate of virologically confirmed recurrences one year post vaccination [84], later studies of glycoprotein vaccines were not effective [85]. Participants with frequent genital HSV-2 recurrences who received a live, attenuated growth compromised strain FDA approved Drug Library cell assay of HSV-2 with a deletion in UL39 (ICP10ΔPK) had decreased self-reported recurrences as compared to placebo [86]. Importantly, this construct was safe, providing proof-of-concept for replication competent vaccine constructs. A replication defective HSV-2 strain with a gH deletion which was able to undergo a single cycle of replication (disabled infectious single cycle, DISC) had similar time to first recurrence, lesion healing rates, and genital shedding rates in HSV-2 seropositive persons with recurrent genital herpes as placebo [87]. Safe and effective prevention of genital HSV infection is the ultimate goal of HSV vaccine research. Because the correlate of protective immunity is unknown, testing the efficacy of prophylactic HSV vaccines requires prospective follow up of persons at risk for genital HSV acquisition. Prior prophylactic vaccine trials have been performed almost exclusively in North America, where

find more the HSV-2 acquisition rate is low. In the per-protocol analysis of the recent gD2 subunit vaccine study, only 1.6% of participants acquired HSV-2 infection, and 1.0% had genital ulcer disease due to HSV-1 or HSV-2, the primary endpoint [82]. In contrast, HSV-2 is rapidly

acquired among men and women initiating sexual activity in sub-Saharan Africa, with incidence up to 23 per 100 person years [88]. Prophylactic HSV-2 vaccine studies should be performed in international settings, where the greatest burden of disease exists. Multi-national trials are also important since there may be geographical strain differences which affect HSV-2 pathogenicity and immunogenicity [89]. It will be important to understand genotypic and phenotypic variation in HSV-2 strains from around the world prior to performing these trials, as these differences may affect vaccine efficacy [89]. Synergy with established out networks, such as the HIV Vaccine Trials Network (HVTN), should be explored. Young women are at highest risk for acquiring HSV-2, and serve as an ideal population for prophylactic vaccine trials. Given the sex differences in vaccine efficacy from the gD2 vaccines, it may be important to power trials to stratify vaccine efficacy by sex. As the efficacy of a vaccine may be different in persons who are HSV-1 seropositive and seronegative, both populations should be evaluated. Importantly, HSV-1 is often acquired early in childhood, especially in resource-limited settings, which may shift the optimal time for vaccination to infancy/early childhood. A vaccine targeting both HSV-1 and HSV-2 could be tested in parallel in HSV-1/HSV-2 seronegative children for prevention of HSV-1 infection.