The failure of an experimental herpes vaccine against the sexually transmitted herpes simplex virus has dashed hopes for widespread use of the treatment.

For reasons that aren’t clear, the vaccine protected against only one of the two types of the sexually transmitted virus — simplex virus type 1, known as HSV1 — researchers reported in the latest issue of the New England Journal of Medicine.

The study of more than 8,000 women aged 18 to 30 found that it didn't protect against simplex virus type 2, known as HSV2.

One in six Americans ages 14 to 49 is infected with HSV2, according to the Centers for Disease Control and Prevention, while federal health figures show that nearly 60 percent of adults in the U.S. are infected with HSV1.

Typically, HSV2 causes lesions and blisters in the genital area. HSV1 generally causes sores in the mouth and lips, although it increasingly has been found to cause genital disease.

According to a statement from Saint Louis University Medical Center and University of Iowa Health Care Marketing and Communications:

There currently is no cure or approved vaccine to prevent genital herpes infection, which affects about 25 percent of women in the United States and is one of the most common communicable diseases. Once inside the body, HSV remains there permanently. The virus can cause severe neurological disease and even death in infants born to women who are infected with HSV and the virus is a risk factor for sexual transmission of HIV.

“I think this is the end of the vaccine,” said coauthor Dr. Peter A. Leone, an infectious disease specialist at the University of North Carolina, Chapel Hill, MSNBC reported “It would be difficult to imagine marketing a vaccine that would only work against HSV1.”

However, said Robert Belshe, M.D., lead author of the study:

“There is some very good news in our findings. We were partially successful against half of the equation – protecting women from genital disease caused by HSV-1. It’s a big step along the path to creating an effective vaccine that protects against genital disease caused by herpes infection. It points us in the direction to work toward making a vaccine that works on both herpes simplex viruses.”

Agreed, said Leone, adding that the findings were a "substantial step forward" in understanding the disease..

“It used to be we’d think HSV1 above the waist, HSV2 below the waist,” Leone said.