HealthDay News — A once-promising investigational vaccine against herpes viruses showed only 20% efficacy against herpes genital disease in a large clinical trial designed to mimic the general population of uninfected women, data published in the New England Journal of Medicine indicate.

The vaccine showed some efficacy against herpes simplex virus type 1 (HSV-1) but not HSV type 2 (HSV-2) genital disease and infection, Robert B. Belshe, MD, of Saint Louis University, and colleagues reported.

“Although the development of a vaccine that provides protection against HSV-1 genital disease is a substantial step forward, additional progress is needed before a herpes vaccine is likely to be approved for general use. Any candidate vaccine will probably have to have proven efficacy against both HSV-1 and HSV-2 disease,” the researchers wrote.

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Belshe and colleagues conducted a randomized, double-blind field trial involving 8,323 women aged 18 to 30 years who were seronegative for HSV-1 and HSV-2. Participants received either the HSV-2 vaccine or a control vaccine that consisted of inactivated hepatitis A vaccine at months zero, one, and six, and were followed for the development of genital herpes disease due to HSV-1 or HSV-2 from one month after the second dose through month 20.

Overall, the HSV vaccine was was just 20% efficacious in preventing genital herpes disease, analysis revealed. It was 58% efficacious against HSV-1 and 35% efficacious against HSV-1 infection (with or without disease). The vaccine was not efficacious against HSV-2 infection, even though it elicited the production of antibodies against HSV-2.The researchers stated that the overall 22% vaccine efficacy was driven by a 35% efficacy against HSV-1 infection.

These results were surprising, as two previous studies demonstrated that the vaccine was 73% and 74% efficacious against genital disease among seronegative women whose male partners were infected with one of the two viruses. “The difference in efficacy is likely to be due to some factor in the two populations studied,” the researchers wrote.

The researchers hypothesized the following reasons for the previously observed vaccine efficacy among women in the discordant couple population:

  • Selection bias for women with relative resistance to HSV-2
  • Potential immunologic priming from chronic sexual exposure to HSV-2 from the infected partner
  • Less frequent sexual activity among couples in long-term relationships compared with couples in new relationships

Different approaches such as a live attenuated vaccine or vaccine vectors may be necessary to effectively prevent herpes simplex virus infection, the researchers suggested.

The study was funded in part by GlaxoSmithKline; several researchers disclosed financial relationships with GlaxoSmithKline and/or other pharmaceutical companies.

Belshe RB et al. N Engl J Med. 2012;366:34-43.