Vaccines and variants: Modelling insights into emerging issues in COVID-19 epidemiology

Mathematical modelling has played a pivotal role in understanding the epidemiology of and guiding pub-lic health responses to the ongoing coronavirus disease of 2019 (COVID-19) pandemic. Here, we review the role of epidemiological models in understanding evolving epidemic characteristics, including the effects of vaccination and Variants of Concern (VoC). We highlight ways in which models continue to pro-vide important insights, including (1) calculating the herd immunity threshold and evaluating its limita-tions; (2) verifying that nascent vaccines can prevent severe disease, infection, and transmission but may be less efficacious against VoC; (3) determining optimal vaccine allocation strategies under efficacy and supply constraints; and (4) determining that VoC are more transmissible and lethal than previously cir-culating strains, and that immune escape may jeopardize vaccine-induced herd immunity. Finally, we explore how models can help us anticipate and prepare for future stages of COVID-19 epidemiology (and that of other diseases) through forecasts and scenario projections, given current uncertainties and data limitations. (c) 2021 Published by Elsevier Ltd.