evidence: For adolescents aged 12 to 17 years, the unvaccinated vs vaccinated IRR against cases declined from 6.7 (95% CI, 6.2-7.2) the week of November 29 to 2.9 (95% CI, 2.8-3.0) the week of December 13 (Omicron 19% sequences), and declined further to 2.0 (95% CI, 1.9-2.2) by January 24 (Omicron >99% sequences) (Table). For unvaccinated vs fully vaccinated children aged 5 to 11 years, the IRR was 3.1 (95% CI, 2.7-3.6) the week of December 13 and declined to 1.1 (95% CI, 1.1-1.2) by January 24. Hospitalizations were higher in unvaccinated than fully vaccinated individuals by the week of January 24, with IRR of 1.9 (95% CI, 0.9-4.8) for children aged 5 to 11 years compared with 3.7 (95% CI, 2.1-6.5) for those aged 12 to 17 years. [...] The risks of infection and hospitalization were elevated for unvaccinated vs vaccinated children aged 5 to 11 and 12 to 17 years, although the risk declined as Omicron became more prevalent. Protection declined with time since vaccination. These results complement recent findings of reduced vaccine effectiveness for adolescents against the Delta variant2 and the dual effects of the variant and waning protection against infection, with sustained protection against hospitalizations.4