Human papillomavirus (HPV) vaccination protects against new HPV infections, but seemingly no impact on the clearance of existing infections. We assessed the association between HPV vaccination and incidence and clearance of HPV infections among sexually active women in the Carrageenan-gel Against Transmission of Cervical HPV trial, conducted in Montreal, Canada (2013-2020). Participants attended seven visits over 12 months, where they provided self-collected vaginal samples and completed questionnaires on risk factors. Participants self-reported their HPV vaccination status at screening, enrollment, and follow-up visits. Samples were genotyped for HPV using the Linear Array assay. We used Cox regression to estimate hazard ratios (HR) and 95 % confidence intervals (CI) for incidence and clearance of HPV infections, with the unit of analysis being the HPV type. Analyses considered stringent (reported in ≥2 sources) and non-stringent (reported in ≥1 source) definitions of vaccination status. HPV types were classified as vaccine-targeted (HPVs 6/11/16/18) and non-vaccine-targeted (within-species: HPVs 31/33/35/39/44/45/52/58/59/67/68/70; cross-species: HPVs 26/34/40/42/51/53/54/56/61/62/66/69/71/72/73/81/82/83/84/89). To control for confounding, we applied inverse probability of treatment weights, based on study and participant characteristics. Of 461 participants, 45.8 % and 55.5 % were vaccinated according to the stringent and non-stringent definitions, respectively. Vaccination was associated with a lower risk of new HPVs 6/11/16/18 detection in the most stringent (HR = 0.41, CI:0.23-0.72) and least stringent (HR = 0.41, CI:0.23-0.72) definitions. Vaccination was not associated with incident within-species (most stringent: HR = 1.21, CI:0.90-1.64; least stringent: HR = 1.10, CI:0.82-1.48) or cross-species (most stringent: HR = 1.21, CI:0.94-1.55; least stringent: HR = 1.11, CI:0.87-1.41) HPV types. Vaccination did not impact clearance of baseline HPVs 6/11/16/18 (most stringent: HR = 1.23, CI:0.47-3.24; least stringent: HR = 1.40, CI:0.57-3.47), within-species (most stringent: HR = 1.50, CI:0.88-2.56; least stringent: HR = 1.58, CI:0.98-2.55) or cross-species HPV infections (most stringent: HR = 0.71, CI:0.49-1.03; least stringent: HR = 0.80, CI:0.56-1.16). We found that HPV vaccination is effective as a prophylactic measure but has no therapeutic effects on existing infections.
Kassam et al. (Sat,) studied this question.