Genocea’s therapeutic genital herpes vaccine posted new phase 2b data that support the candidate's "groundbreaking potential" as possibly the first genital herpes treatment advancement in more than 20 years, the biotech's CEO says.

The candidate, GEN-003, combines an antigen with an adjuvant and in this trial, significantly reduced the rate of genital lesions six months after dosing. In the 131-patient study, a small dose reduced the number of days patients experienced lesions to 4.5% from 7.9% in the placebo arm, a 41% improvement.

Results from the phase 2b study—plus a separate phase 2 trial—have steered the company toward testing that smaller dose in its phase 3 study, which Genocea plans to launch in the fourth quarter. The new trial proved the potential of GEN-003 "to be the first-ever therapeutic vaccine for a chronic infection and the first advance in the treatment of genital herpes in more than 20 years," CEO Chip Clark said in a statement.

Lesion rate was a secondary clinical endpoint for the latest study, but those stats are important to both patients and their caregivers, especially in terms of treatment experience.

During the 310-participant phase 2 study, the results of which were published in March 2016, the vaccine delivered solid results on its primary endpoint of viral shedding rate. At a six-month and 12-month post-treatment analysis, the smaller dose of the vaccine reduced the shedding rate by 46% and 64% respectively, compared with placebo. For the larger dose, the reductions versus placebo were 58% and 52%.

Another difference between the recently posted phase 2b and previous phase 2 is that lesion data were collected daily throughout the trial. Previous studies on GEN-003 only collected data during 28-day observation periods before and after designated dates.

Most herpes simplex virus infections in the U.S. are caused by HSV type 2, which GEN-003 is targeting. Genocea estimates that about 4.5 million patients in the U.S. currently treat genital herpes with oral antivirals only when the symptoms surface, which doesn't prevent transmission of the virus. 

With Genocea's estimation of a 400 million affected population worldwide, the biotech expects that the shot could reach $2 billion in global revenue.

Future trials could also test GEN-003 in combination with oral antivirals.