RT Journal Article SR Electronic T1 HPV vaccine strategies: the cost of HPV and the choice of vaccine JF Sexually Transmitted Infections JO Sex Transm Infect FD BMJ Publishing Group Ltd SP 315 OP 316 DO 10.1136/sti.2008.034793 VO 85 IS 5 A1 Sheldon R Morris YR 2009 UL http://sti.bmj.com/content/85/5/315.abstract AB