Projections of human papillomavirus (HPV) vaccination impact in Ethiopia, India, Nigeria, and Pakistan: a comparative modelling study

Abstract Background Cervical cancer is the second most common cancer among women in Ethiopia, India, Nigeria, and Pakistan. However, of these four countries, only Ethiopia has introduced human papillomavirus (HPV) vaccination at the national level in 2018 and India in a few states in 2016. Our study objective was to estimate the potential health impact of HPV vaccination among ten cohorts of 9-year-old girls from 2021–2030 in Ethiopia, India, Nigeria, and Pakistan using two independent mathematical models, and assess similarities and differences in vaccine impact projections through comparative modelling analysis. Methods Using two widely published models (Harvard and PRIME) to estimate HPV vaccination impact, we simulated a vaccination scenario of 90% annual coverage among 9-year-old girls from 2021–2030 in Ethiopia, India, Nigeria, and Pakistan. We estimated the potential health impact in terms of cervical cancer cases, deaths, and disability-adjusted life years (DALYs) averted among vaccinated cohorts from the time of vaccination until 2100. We also conducted a comparative modelling analysis to understand the differences in vaccine impact estimates generated by the two models. Results Prior to harmonising model assumptions, the range between the PRIME model and the Harvard model for the potential health impact of HPV vaccination in terms of the number of cervical cancer cases averted among girls vaccinated 2021–2030 between the year of vaccination and 2100 was: 262,000 to 270,000 in Ethiopia; 1,640,000 to 1,970,000 in India; 330,000 to 336,000 in Nigeria; and 111,000 to 133,000 in Pakistan. When harmonising model assumptions, alignment on HPV type distribution significantly narrowed the differences in vaccine impact estimates. Conclusions The main difference in estimates for cases, deaths, and DALYs averted by vaccination between the models are due to variation in interpretation around data on cervical cancer attribution to HPV-16/18; differences in estimates for DALYs averted are additionally due to differences in age-specific remaining life expectancy over time between the two models. As countries make progress towards the World Health Organization targets for cervical cancer elimination, continued explorations of underlying differences in model inputs, assumptions, and results when examining cervical cancer prevention policy will be critical.