Home » Resources Library » Porras C, et al. Efficacy of the bivalent HPV vaccine against HPV16/18-associated precancer: long-term follow-up results from the Costa RicaVaccine Trial. Created: Oct 2023 Porras C, et al. Efficacy of the bivalent HPV vaccine against HPV16/18-associated precancer: long-term follow-up results from the Costa RicaVaccine Trial.