Human papillomavirus vaccine trials and tribulations: Clinical perspectives. 
Human papillomavirus (HPV) affects hundreds of millions of people worldwide and is associated with both benign and malignant neoplasms in men and women.  It is a double-stranded DNA virus with an icosahedral capsid.  Forty HPV types are known to infect mucosal keratinocytes.  If not cured by the immune system, the infection can lead to genital warts, mucosal dysplasia, or cancer.  The most common oncogenic types are 16 and 18.  The vaccine to prevent HPV and its associated morbidity and mortality has existed since 2006.  Several variations protect against an increasing number of HPV types.  The recommended vaccination age is before sexual exposure; administration of the vaccine to children has been controversial.  This continuing medical education review evaluates the current HPV vaccines available to clinicians.  Part I focuses on the debate over who should be vaccinated, at what age, and in which populations.