An effort that began eight years ago to develop a herpes simplex vaccine for women has ended in failure and uncertainty. After assessing final Phase III trial results, the GlaxoSmithKline (GSK) vaccine, known as Simplirix, failed to meet its primary endpoint, which was preventing genital herpes. However, it remains unclear why the vaccine was not effective. Safety issues were not cited as a problem.
The outcome is a huge disappointment for the drugmaker, which has been attempting to expand its portfolio of vaccine products, given that an estimated one in four women in the US alone has genital herpes. In other words, the afflication is one of the most common infectious diseases and that can translate into huge revenues.
The study, which was a randomized, double-blind trial, was undertaken with the US National Institute of Allergy and Infectious Diseases, and tested 8,323 women between 18 and 30 years old, who were tested at 50 sites in the United States and Canada. Participants received either Simplirix or a version of Havrix, an FDA-approved vaccine for thwarting hepatitis A that is sold by Glaxo (see the NIAID statement and a question-and-answer from the agency).
Earlier studies were encouraging. These involved men and women who did not have genital herpes but whose sexual partners were known to be infected, and the vaccine prevented genital herpes disease in more than 70 percent of the female volunteers although there was no clear effect in men. Moreover, Simplirix reduced the risk of developing antibodies to herpes, which are used as an indicator that a person has been infected with HSV, by 40 percent.