Home » Resources Library » Sierra MS, et al. Risk Factors for Non-Human Papillomavirus (HPV) Type 16/18 CervicalInfections and Associated Lesions Among HPV DNA-Negative Women VaccinatedAgainst HPV-16/18 in the Costa Rica Vaccine Trial. Created: Oct 2023 Sierra MS, et al. Risk Factors for Non-Human Papillomavirus (HPV) Type 16/18 CervicalInfections and Associated Lesions Among HPV DNA-Negative Women VaccinatedAgainst HPV-16/18 in the Costa Rica Vaccine Trial.