We would like to acknowledge the investigators, nurses, field workers and other personnel who contributed to the conduct of this trial; Mary Rusizoka, Beatrice Kamala, Wilbroad Shangwe, Francesca Lemme, Serafina Soteli, Clemens Masesa, and the HPV-021 trial team in Mwanza; Pius Magulyati, and the laboratory staff of the National Institute for Medical Research (NIMR) Mwanza Research Centre laboratory; the administrative staff of the Mwanza Intervention Trials Unit (MITU), NIMR Mwanza Research Centre, and Sekou Toure Hospital; Lucy Bradshaw, Gillian Devereux, Jayne Gould and Sue Napierala Mavedzenge and the research support staff at the London School of Hygiene and Tropical Medicine

(LSHTM). We thank Peter Hughes and the Clinical Diagnostic Laboratory of the MRC/UVRI Uganda Research Unit in Entebbe, Selleck GSK1349572 and David Warhurst and the Department of Pathogen Molecular Biology at LSHTM for their contributions to this work. We are grateful to the Ministry of Health and Social Welfare for granting permission to conduct this study. Conflict of interest statement Dr. Watson-Jones and Dr. Mayaud have received grant support through their institutions from GlaxoSmithKline Biologicals SA. During the trial, partial salary support for Drs. Watson-Jones,

Andreasen, Brown and Kavishe came from GSK Biologicals. There are no other conflicts of interest. Dr. Brown is supported by NIH-NIHM 1K01MH100994-01 and NIH-NCATS 8KL2TR000143-08. Richard Hayes, Saidi Kapiga, Selinexor and Kathy Baisley receive support from the MRC and DFID (G0901756, MR/K012126/1). “
“Human papillomavirus (HPV) vaccines induce type-specific neutralizing antibodies which correlate with immunity to the corresponding HPV types [1], and World Health Organization guidelines recommend that assays which assess neutralization be used as the reference standard for measuring HPV vaccine responses [2]. Quadrivalent HPV (Q-HPV) also vaccine (Gardasil®, Merck Laboratories) consists of HPV 6, 11, 16 and 18 virus-like particles (VLP) and is licensed for a 3-dose

regimen. Post-Gardasil® antibody responses are typically measured by a proprietary multiplex competitive Luminex immunoassay (cLIA) [3], which is based on competitive binding of type-specific HPV antibodies in human sera with labelled monoclonal antibodies directed against neutralizing epitopes of the respective VLP types (HPV 6, 11, 16 and 18). It has been reported that HPV antibodies measured by the cLIA may decline to become undetectable over time, especially for HPV 18, despite continued vaccine efficacy in preventing infections [4] and [5]. The significance of the loss of detectable antibodies is unknown as protective levels of HPV antibodies remain undefined [1], [6] and [7] and vaccine efficacy remains near 100%. Recently, Merck Laboratories developed a total IgG Luminex immunoassay (TIgG) which measures antibodies against the entire VLP, i.e.