Herpes Simplex Virus Shedding Rate: Surrogate Outcome for Genital Herpes Recurrence Frequency and Lesion Rates, and Phase 2 Clinical Trials End Point for Evaluating Efficacy of Antivirals

Background: We tested whether genital herpes simplex virus (HSV) shedding is an appropriate surrogate outcome for the clinical outcome of genital herpes lesions in studies of HSV-2 antiviral interventions. Methods: We analyzed prospective data from natural history studies and clinical trials of antiviral agents for HSV-2 in which HSV-2-seropositive participants provided self-collected anogenital swab specimens daily over ≥25 days for HSV DNA quantitation by polymerase chain reaction (PCR). Genital recurrences were self-reported. Results: Among 674 participants, genital HSV shedding was detected on 17% of days, and genital lesions were reported on 10% of days. Within the same session, HSV shedding rates were strongly correlated with lesion rates (ρ = 0.61, P < .0001). The relative reduction in the recurrence rate was 72% (P = .041) for recipients of the antiviral agent pritelivir as compared to recipients of placebo, but it decreased to 21% (P = .75) after adjustment for HSV shedding rate. When evaluating valacyclovir and acyclovir, adjustment for the HSV shedding rate also led to a reduced association of these antivirals with the recurrence rate. Overall, 40%-82% of the antiviral effect on recurrences was explained by its effect on HSV shedding. Conclusion: HSV genital shedding measured by PCR analysis in swab specimens self-collected daily is an appropriate surrogate outcome for genital herpes lesions because it is in the causal pathway to recurrences.