Long-term immunogenicity, effectiveness, and safety of nine-valent human papillomavirus vaccine in girls and boys 9 to 15 years of age: Interim analysis after 8 years of follow-up oleh Sven-Eric Olsson, Jaime Alberto Restrepo, Julio Cesar Reina, Punnee Pitisuttithum, Angels Ulied, Meera Varman, Pierre Van Damme, Edson Duarte Moreira, Jr., Daron Ferris, Stanley Block, Oliver Bautista, Nancy Gallagher, Jennifer McCauley, Alain Luxembourg