that emerged in the UK with the second COVID-19 wave in late 2020. The efficacy of currently licensed COVID-19 vaccines against B. 1.617. 2 is unknown; although it possesses 12 mutations in its spike protein relative to the wildtype SARS-CoV-2 first detected in Wuhan, China, in December, 2019, B. 1.617. 2 lacks mutations at amino acid positions 501 or 484 in its ACE2 receptor-binding domain, commonly associated with VOCs (appendix p 2) or escape from neutralising antibodies (NAbs).

To determine vaccine-induced NAb escape by B. 1.617. 2 and compare activity to previous strains with existing estimates for population-based vaccine efficacy, we carried out an initial analysis of the Legacy study, established in January, 2021, by University College London Hospital and the Francis Crick Institute in London, UK, to track serological responses to vaccination in prospectively recruited staff volunteers (appendix p 6). A detailed description of the methods, including the clinical cohort, virus culture conditions, genetic sequencing, and neutralisation assays, and the statistical analysis are available in the appendix (p 8). The Legacy study was approved by London Camden and Kings Cross Health Research Authority Research and Ethics committee (IRAS number 286469) and sponsored by University College London.