Fig. 1.

SARS-CoV-2 Omicron infection incidence and risk. In Panel A, time to SARS-CoV-2 Omicron infection from July 1 through September 13, 2022, was estimated in individuals with one prior Omicron infection (i.e., between December 15, 2021 and June 30, 2022, with no pre-Omicron infections), one pre-Omicron infection (i.e., infection prior to December 15, 2021), multiple prior infections (i.e., prior to and/or between December 15, 2021 and July 1, 2022), and no prior infections (i.e., no infections between March 2020 and June 30, 2022), by means of the Kaplan–Meier method. Statistical significance between the curves was determined by log-rank test. Shading around the mean line indicates the 95% confidence interval. The dotted horizontal-vertical line indicates 50% cumulative incidence. In Panel B, the Cox proportional-hazards regression model was used to estimate hazard ratios of Omicron infection between July 1 and September 13, 2022, with the baseline hazard on July 1, 2022. Variables (age, sex, previous infection, mRNA vaccine combination, residence type, number of outbreaks, clinical frailty scale, time since fourth vaccination) reflect characteristics at baseline, with adjustments for study site. The hazard ratios are presented with 95% confidence intervals based on robust standard errors.