Vical plummets on placebo promise in herpes study

San Diego-based Vical's stock was cut almost in half on 23 June after the company reported that the placebo in a Phase I/II clinical trial outperformed both the monovalent and bivalent forms of its therapeutic genital herpes vaccine by a wide margin. In terms of the trial's primary endpoint, viral shedding decreased 12% for patients treated with the monovalent vaccine, 19% in the study's bivalent arm and 45% in the placebo group.

Changes in lesion rate and viral load – secondary endpoints in the study – were statistically significant, so longer-term safety...