The largest study to date of a Genital herpes vaccine under development by GlaxoSmithKline shows it is safe, well tolerated and produces an immune response.

The antibody response seen with the vaccine, based on a surface protein of herpes simplex virus (HSV) 2, is at least as strong as that seen with natural infection, told Dr. David I. Bernstein of Cincinnati Children’s Hospital Medical Center.

However, “Since we don’t know what protects you from getting genital herpes, it’s still difficult to say what correlation there would be from the responses we measured” in protecting against infection, he added.

Past trials of the vaccine found it protected women, but not men, from contracting herpes, and it only worked for women who had not been infected previously with HSV-1, the herpes virus that causes cold sores.

The current study, reported in the journal Clinical Infectious Diseases, involved 7,460 men and women and was intended to explore the effects of gender and prior HSV infection on immune responses.

While the vaccine did produce local reactions including soreness, the researchers found, these reactions were no worse among people already positive for HSV 1 or 2, and also did not increase after the second or third injection.

This finding is important, Bernstein noted, because many people are HSV-1 positive.

One issue in giving the vaccine would be whether recipients should be screened for the virus beforehand. Such screening could be “cumbersome,” he pointed out. “I think they would try to find a young age when there aren’t that many women who are seropositive already. That’s clearly one of the decisions that will have to be made, whether to screen or not to screen and at what age to give the vaccine.”

Compared to natural infection, the researchers found, the vaccine produced higher HSV antibodies. By 13 months after immunization, antibody levels had decreased but were still higher than those seen with natural HSV 2 infection.

“That’s one of the big unanswered questions that we’ll need to find out - how long these antibodies last and whether they’ll provide protection.” Bernstein said.

He and his colleagues note that ongoing trials will determine the effect of the vaccine “in adolescent and preadolescent female subjects, the target population for immunization.”

SOURCE: Clinical Infectious Diseases, May 1, 2005.