Figure 4. Summary of basecase model fits and projections and key results on uncertainty, behaviour, booster vaccinations and waning immunity.

(a) The number of COVID-19 hospital admissions in England, for the basecase scenario, between March 2020 and December 2022. Black lines show reported data, provided by UKHSA. Coloured lines and shaded areas show medians, 50% and 90% interquantile ranges from the fitted model and from the model projection. (b) PCR prevalence in England, for the basecase scenario, between March 2020 and December 2022. The black ribbons show 95% confidence intervals for PCR prevalence data. Coloured lines and shaded areas show medians, 50% and 90% interquantile ranges from the fitted model and from the model projection. (c) The fitted and projected number of COVID-19 deaths in England between March and December 2022, shown for the very high waning scenario (see Table S4). The black line shows the median trajectory of COVID-19 deaths in England over time, with the shaded areas showing the 50% and 90% interquantile ranges. Individual model trajectories are plotted in coloured lines. (d) The effect of future behaviour on COVID-19 deaths and cumulative deaths (thousands) over time is shown with four scenarios for future mobility: a 3-week, a 3-month and a 6-month return to baseline levels, and a no change scenario (see Table 1). (e) The effect of booster vaccination policy on cumulative infections and deaths since October 2021 is shown with four scenarios for booster policies (Table 1). (f) The effect of waning immunity on cumulative infections and deaths between March and December 2022 is shown with three scenarios for waning (Tables 1, S4). The basecase scenarios (shown in panels a and b) and scenarios marked with an asterisk (*) are equivalent.