Researchers have made the first vaccine that protects against genital herpes. But there is a major catch: It works only in women and only if they have never had cold sores.
The findings, reported today, are a surprise. Until now, no vaccine has ever been shown to work in one sex but not the other. Experts say this could present unexpected trouble for creating other vaccines for sexually transmitted diseases, such as AIDS.
More Testing Probably Required
The results were not the clear home run that the vaccine’s developer, SmithKline Beecham, had hoped when it began designing the latest studies a decade ago. Further testing will almost certainly be required for the drug to be approved, assuming that the company keeps working on the product.
Nevertheless, doctors say a vaccine that offers even partial protection against a chronic disease is noteworthy. The only other sexually transmitted disease that can be stopped with a vaccine is hepatitis B.
“I would say the chances are good but not at all certain” that the herpes vaccine will eventually be approved for routine use, said Dr. Spotswood Spruance of the University of Utah, one of those who tested it.
He predicted the vaccine would be given to adolescent girls. Widespread use of the vaccine this way would probably reduce genital herpes for both sexes, since it would lower the chance of men coming in contact with infected females.
Herpes Lasts a Lifetime
Genital herpes and cold sores result from closely related bugs. Herpes simplex virus type 1, or HSV-1, causes fever blisters on the mouth, while HSV-2 triggers sores on the genitals. Once acquired, both infections last a lifetime.
Both infections grow more common with age. Recent surveys suggest that in the United States, 45 million people ages 12 and older are infected with the genital herpes virus.
Spruance and colleagues reported the results of two major studies of the vaccine at a meeting in Toronto of the American Society for Microbiology. Both were conducted on couples in which one partner had genital herpes but the other did not. The studies involved more than 2,700 people in the United States, Canada, Australia, Italy and New Zealand.
In one of the studies, the partners who were free of genital herpes had never been infected with either HSV-1 nor HSV-2, while the other included those who had HSV-1 but not HSV-2.
During 19 months of follow up, it turned out that the vaccine did nothing to protect men or to protect women who already had HSV-1. However, it was about 75 percent effective in warding of genital herpes sores in women who had never had either form of the virus.
About 3 percent got genital herpes after taking the vaccine, compared with about 11 percent of those receiving dummy shots. Another 3 percent of those getting the vaccine became infected but never developed genital sores.
The researchers said that being infected with HSV-1 probably helps protect people from getting genital herpes, and the vaccine does little to increase this natural barrier.
Why Only Women?
Why the vaccine works in women but not men is unclear, although the researchers said it probably has something to do with differences in sexual anatomy. Perhaps the vaccine boosts the immune system so it can attack the herpes virus while still in the vagina, but it is unable to stop the virus after it gains access to the bloodstream through tiny tears in the penis.
“The results are not exactly what we expected,” said Gary Dubin, who heads adolescent vaccine development for SmithKline Beecham in Belgium. He said the company is getting reaction from regulators and public health officials before deciding what to do next.
However, Spruance said the vaccine could be targeted at girls ages 10 to 13. At this age, he said, about half have not been infected with either form of the herpes virus and so could benefit from the vaccine.
Despite its drawbacks, the vaccine “really looks very effective. It seems potentially useful,” commented Dr. William Craig of the University of Wisconsin, head of the conference program committee.
The vaccine is made from a protein taken from the outer surface of the herpes virus. It is combined with a bacterial toxin that acts as an immune system booster.