NEW YORK The future of vaccines, infectious disease experts say, is teenagers. Parents are used to the idea of their babies getting up to 20 vaccinations by age 2 to prevent polio, measles, chickenpox and other diseases transmitted by coughing. But pharmaceutical companies are inventing new vaccines against diseases usually transmitted by sex, drug use, foreign travel or living in dormitories or barracks. Half a dozen are now in the long and tangled medico-regulatory pipeline between the petri dish and the pediatrician's syringe. "Adolescent vaccines are the next wave," Michael Decker, vice president for scientific affairs at the vaccine subsidiary...