Effect of the incremental protection of previous infection against Omicron infection among individuals with a hybrid of infection- and vaccine-induced immunity: a population-based cohort study in Canada

•Previous SARS-CoV-2 infections confer added benefits in reducing Omicron reinfection risk.•The incremental immunity acquired from past infections waned within 1 year.•Infection-acquired immunity has limited influence on shield-effects at the population level.•This is one of the largest cohort studies to examine infection-acquired immunity.