Butler, J., Nath, M., Blana, D., Ball, W., Beech, N., Black, C., Osler, G., Peytrignet, S., Wilde, K., Wozniak, A. & Sawhney, S. 2021, 'The clinically extremely vulnerable to COVID: identification and changes in healthcare while self-isolating (shielding) during the coronavirus pandemic {pre-print}', medRxiv. https://doi.org/10.1101/2021.09.09.21263026