FIGURE 2—

Smoothed Weighted SARS-CoV-2 Swab-Positivity Prevalence From All Rounds of the REACT-1 Study by (a) Overall Prevalence, (b) Age Groups, and (c) Region: England, May 1, 2020–March 31, 2022

Note. REACT-1 = REal-time Assessment of Community Transmission-1; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2. We used the random iterative method (RIM) weighting approach to correct for possible nonresponse bias and ensure that our prevalence estimates were representative of the population of England as a whole. Using a Bayesian penalized-spline model fit to the daily swab-positivity data, we estimated the median (plain line) and 95% credible intervals (shaded regions) of weighted prevalence throughout the study period. Results are shown for the full population of England (A) with model fit on rounds 1–7, 8–13, and 14–19, separately, and for 4 broad age groups (B): 5–17 y, 18–34 y, 35–54 y, and 55 y and older, and by region (C), with model fit throughout the duration of the study. Ranking of weighted prevalence by age and region changed over the course of the epidemic in England. For example, there was particularly high prevalence in those aged 5 to 17 y in October 2021 and January 2022.