Fig. 4: Dominant SARS-CoV-2 variants, vaccinations, infections and deaths since early 2020 in the UK.

a, Waves of dominant variants in the UK (B.1, B.1.1.7/Alpha, B.1.617.2/Delta, AY.4.2/Delta and Omicron sublineages BA.1, BA.2, BA.4 and BA.5), proportion of the UK population with one or two doses and with one booster vaccination, number of COVID-19 cases and number of reported COVID-19-related deaths. Data from COG-UK Mutation Explorer¹⁹² and GOV.UK. b, Diagrammatic visualization of the dynamic relationship between variant transmissibility, antigenicity, virulence and fitness. As population immunity derived from infection and vaccination increases, the fraction of completely immunologically naive hosts declines (gradient blue lines). Consequently, the importance of antigenic novelty in determining variant fitness increases. Antigenic distance to previously circulating variants becomes an increasingly key determinant of variant transmissibility, increasing the potential for intrinsic and real-world transmissibility to diverge. Similarly, antigenic distance influences a variant’s potential to infect and cause disease in immune hosts, increasing the potential for a variant’s intrinsic virulence to diverge from its real-world clinical impact. VOC, variant of concern.