Pharmaceutical and biotechnology companies are increasingly developing drugs and vaccines for sexually transmitted diseases (STDs) other than HIV. The success of AIDS drugs are helping the search by giving researchers time to work on other diseases and by providing a blueprint to follow. The U.S. market for a vaccine for a common STD could be over $1 billion annually. A potentially powerful vaccine for human papilloma virus helps make Merck the major player in STD treatments, although GlaxoSmithKline is also working on a vaccine for the disease.