The news this fall about herpes was startling: If nothing was done to stop it, virtually half of all young women in America were projected to contract genital herpes by 2025.

     This explosion of herpes — 39 percent of young men were also projected to become infected — could raise annual associated costs from $1.8 billion to $2.7 billion, said Dr. David N. Fisman, co-author of a report in the October issue of Sexually Transmitted Diseases, the journal of the American Sexually Transmitted Diseases Association.
     However, news of a promising herpes vaccine has put these dire projections on hold.
     The vaccine, which prevented infections in 74 percent of women who had neither genital herpes nor the virus that causes cold sores, is "incredibly exciting," said Dr. Fisman, a public health official in Hamilton, Ontario.
     "So rather than being pessimistic, I'm actually optimistic that the future is not going to look like our model," he said last week.
     Genital herpes is one of the most pervasive sexually transmitted diseases in the United States, with an estimated 45 million infected people.
     The virus-caused infection is spread by skin-to-skin contact, even when an infected person shows no symptoms. It is incurable, but there are drugs to treat the painful and itchy sores that erupt in the genital area and last for weeks.
     The virus is especially dangerous if contracted in late pregnancy, as it can be passed to a newborn, causing severe cognitive damage or death.
     Herpes infections also heighten the risk of contracting HIV, the virus that causes AIDS.
     The new herpes vaccine, reported in the Nov. 21 issue of the New England Journal of Medicine, was tested on 1,867 persons who didn't have the genital herpes virus and 847 people who had neither genital herpes nor the virus that causes cold sores. All the subjects were in sexual relationships with someone who had genital herpes.
     The GlaxoSmithKline Biologicals' vaccine was considered effective among women who had neither kind of herpes virus, blocking infection in 74 percent of these women.
     The vaccine was not considered effective among women who had the cold-sore type of herpes virus nor among men in either group.
     A national trial for the herpes vaccine was announced last month by the National Institutes for Health.
     If successful, the herpes vaccine could be given to girls around the age of 11, researcher Dr. Lawrence R. Stanberry told Reuters news agency last month. Even with the vaccine's limitations, "you would eventually see an impact on the spread of herpes in both men and women," he said.
     The herpes vaccine is one of three "potential blockbusters" for the treatment of STDs, said Dr. David Soper, a professor at the Medical University of South Carolina.
     The other two vaccines, he said, are one that appears to block a dangerous strain of human papilloma virus (HPV), which causes cervical cancer, and one that may block infertility-causing chlamydia.
     "I'm very optimistic" about the herpes and HPV vaccines, said Dr. Peter Leone, associate professor of medicine at the University of North Carolina.
     "The challenge," he added, "will be acceptability," whether the general public will support vaccines for children when they know it's to prevent STDs.
     "Vaccines may be able to limit" the spread of STDs, "but we have to be careful that we don't give people a false sense of security," cautioned Pia de Solenni, an analyst with the Family Research Council.
     "We still need to push for behavioral changes," such as sexual abstinence before marriage and monogamy after marriage, she said. "People in monogamous relationships, by and large, do not have the rates of STDs that other people do."