Home » Resources Library » Safaeian M, et al. Costa Rica HPV Vaccine Trial (CVT) Group. Durability of Protection Afforded by Fewer Doses of the HPV16/18 Vaccine: The CVT Trial. Created: Oct 2023 Safaeian M, et al. Costa Rica HPV Vaccine Trial (CVT) Group. Durability of Protection Afforded by Fewer Doses of the HPV16/18 Vaccine: The CVT Trial.