Orestis A Panagiotou,1 Brian L Befano,2 Paula Gonzalez,3,4 Ana Cecilia Rodríguez,3 Rolando Herrero,4 John T Schiller,5 Aimée R Kreimer,1 Mark Schiffman,1 Allan Hildesheim,1 Allen J Wilcox,6 Sholom Wacholder,1 on behalf of the Costa Rica HPV Vaccine Trial (CVT) Group (see end of manuscript for full list of investigators)