Merck's vaccine pipeline is a gusher! Last year its therapeutic HIV vax made headlines. Now, in December's New England Journal of Medicine, comes news that its preventive vax against HPV-16, a common strain of the virus that causes cervical cancer -- a top killer of HIVers -- has proved 100 percent effective. In a study of 1,500 young women, the inoculated half remained HPV free, while the placebo half saw 50 infections or worse. Two probs: Vax doesn't vanquish all HPV strains, plus it's five years off.