GSK herpes vaccine fails major trial

GSK’s HerpeVac vaccine against herpes simplex is likely to be discontinued following a major phase III clinical trial that showed it to be ineffective in protecting women against either infection or genital symptoms.

In a trial of over 8,000 women, HerpeVac was found to be partly effective against the HSV-1 strain of the herpes virus but ineffective against the HSV-2 strain, which is more dangerous and clinically indistinguishable.

The trial results contrast with earlier findings that the vaccine showed strong efficacy against both strands of the virus in women whose regular partners had the disease.

“I think this is the end of the vaccine,” said study co-author Dr. Peter Leone of the University of North Carolina. “It would be difficult to imagine marketing a vaccine that would only work against HSV-1.”

The phase III study, sponsored by GSK and the National Institute of Allergy and Infectious Disease, enrolled 8,323 women aged 18–30 who were seronegative for herpes simplex antibodies. They were given three doses of HerpeVac, or a hepatitis vaccine as control, over six months.

The vaccine was found to be 35% effective against infection with HSV-1 and 58% effective in preventing genital symptoms from it, but wholly ineffective against HSV-2. Overall, this meant that it prevented infection in 22% of cases and prevented genital disease in 20%.

Two earlier studies had shown HerpeVac to be 73% and 74% effective in preventing genital disease from HSV-2 in seronegative women with seropositive long-term partners. It has been speculated that these women had already developed a certain level of immunity.

Dr Leone commented that the vaccine would probably have a limited public health benefit, and so will not be put on the market.