Efficacy and other milestones for human papillomavirus vaccine introduction

Last year, the World Health Organization (WHO) convened a gathering of experts, including scientists, national regulatory authorities, industry representatives, epidemiologists and government officials from both developed and developing countries to discuss appropriate endpoint measurements for HPV vaccine efficacy and effectiveness trials. The consultation also considered the regulatory requirements and public health issues that vaccine candidates should address before deployment, particularly in developing countries. This report summarizes the discussions and the conclusions reached over the course of the consultation. The general consensus of the consultation was that it would be desirable to have a globally-agreed, measurable efficacy endpoint for considering deployment of HPV vaccines in public health settings. After hearing from experts about virological and clinical endpoints to be considered, requirements of regulatory authorities of various countries and endpoints used to measure efficacy and effectiveness for another known cancer vaccine (hepatitis B), the experts agreed that ethical and time considerations make it necessary to use a surrogate endpoint, and not invasive cervical cancer, to define efficacy of HPV vaccines. While regulatory authorities of each country ultimately will determine the endpoints required for licensure, the consultation recommended that the endpoint for efficacy in population-based studies be, based on current knowledge, histologically-classified cervical intraepithelial neoplasias (CIN) of moderate or high-grade, as well as cancer. Since persistent infection with the same high-risk type is considered a predictor for moderate or high-grade cervical dysplasias and cancer, they might represent a useful endpoint in future vaccine efficacy studies. Indeed, if vaccines prove to be effective against transient or persistent HPV infections, it is likely that they will protect women against cervical cancer. The consultation recognized that in the context of many developing countries, efficacy alone might not provide enough information for countries to decide whether or not to adopt HPV vaccines as a public health prevention tool against cervical cancer. The consultation unanimously agreed that additional clinical bridging studies as well as studies to clarify local epidemiology should be conducted in certain developing countries to determine the potential impact of vaccination. Such countries should also undertake targeted interventions to ensure acceptability and programmatic feasibility of the vaccination. Recognizing that upon vaccine introduction it will be some years before a reduction in cervical cancer is detectable at the population level, the consultation stressed the importance of maintaining existing cervical screening programmes while such long-term studies are conducted. The following paper explains the background and rationale behind these conclusions and elaborates on specific considerations for vaccine study and introduction in developing countries.