Journal of the American Medical Association (07/28/99) Vol.
Investigators for the Chiron HSV Vaccine Study Group found
that protection from herpes simplex virus type 2 (HSV-2) will
require vaccines to do more than induce high levels of
specific neutralizing antibodies. The researchers conducted
two randomized, double-blind, placebo-controlled multicenter
trials of a recombinant subunit vaccine against the virus.
The vaccine contained gB2 and gD2, HSV-2 surface proteins
against which neutralizing antibodies are directed. Subjects
were vaccinated at months 0, 1, and 6. Participants in the
control group received a citrate buffer vehicle, and all
subjects were followed up after the third immunization.
Researchers measured outcome by time to acquisition of HSV-2.
During the first five months of the trial, those receiving the
vaccine had a 50 percent lower acquisition rate than the
controls. According to the data, the acquisition rate of HSV-
2 for vaccinated subjects was 4.6 per 100 patient years,
compared to 4.2 per 100 patients years in those receiving the
placebo. Although the vaccine induced high levels of HSV-2
specific neutralizing antibodies in all subjects, follow-up
study revealed that the vaccine had no significant influence
on duration of clinical first episodes of genital HSV-2 or
frequency of reactivation. Furthermore, overall vaccine
efficacy was 9 percent. The researchers assert that an
effective vaccine must have a higher efficacy level than 9
percent and should do more than stimulate high levels of
specific neutralizing antibodies.