Herpevac (gD2 subunit, GSK)

What it is

Herpevac was a prophylactic (preventive) protein-subunit vaccine developed by GlaxoSmithKline. It was built around a single HSV-2 protein — glycoprotein D (gD2) — combined with two adjuvants, alum and MPL. The idea was that antibodies against gD2 would stop the virus from entering cells and thereby prevent genital herpes.

Where it stands

Herpevac was tested in a large Phase 3 trial, the “Herpevac Trial for Women” (NCT00057330), enrolling about 8,300 women who were seronegative for both HSV-1 and HSV-2. The results, published in the New England Journal of Medicine in 2012, were pivotal — and instructive about the distinctions this site emphasizes:

• Against HSV-2 genital disease — the vaccine’s actual target — it was not effective (about 20% efficacy, not statistically significant).
• Against HSV-1 genital disease it was unexpectedly protective, with roughly 58% efficacy.

Later laboratory work suggested why: HSV-2’s gC2 and gE2 proteins blunt the antibody response that gD2 alone provokes, whereas HSV-1’s equivalents do not. This helped motivate the multi-protein (trivalent) designs that came after. GSK did not advance Herpevac, so the program is inactive. It stands as evidence that a vaccine can succeed against one herpes type while failing against another — which is exactly why HSV-1 and HSV-2 must never be treated as interchangeable.