Vical abandons HSV-2 vaccine development on disappointing trial results

US drug developer Vical’s (Nasdaq: VICL) shares were down as much as 31% on Monday, trading below $1.20, after it revealed it is dropping development of its genital herpes vaccine. The company's stock has fallen 50% in the last year, and is well off its five-year high of $45.10 per share.

The company announced top-line results from a randomized, double-blind, placebo-controlled, Phase II clinical study of its therapeutic bivalent vaccine candidate for herpes simplex virus type 2 (HSV-2) did not meet its primary endpoint of annualized lesion recurrence rate calculated based on those genital recurrences that were both clinically- and virologically-confirmed during a minimum of nine months of surveillance.

The Phase II study was conducted in 261 healthy HSV-2 seropositive adults, 18 to 50 years of age, with a self-reported history of 4 to 9 recurrences per year. Subjects were randomized 2:1 to receive either vaccine or placebo. The vaccine was generally safe and well tolerated, as assessed by an independent safety monitoring board; there were no grade 4 adverse events or serious adverse events reported related to vaccination.