BibTex format
@unpublished{Williams:2021:10.1101/2021.07.30.21260912,
author = {Williams, LR and Ferguson, NM and Donnelly, CA and Grassly, NC},
doi = {10.1101/2021.07.30.21260912},
publisher = {Cold Spring Harbor Laboratory},
title = {Measuring vaccine efficacy against infection and disease in clinical trials: sources and magnitude of bias in COVID-19 vaccine efficacy estimates},
url = {http://dx.doi.org/10.1101/2021.07.30.21260912},
year = {2021}
}