Predominant risk factors for COVID-19 hospitalisation included previous infections (bacterial infection, tonsillitis, and pneumonia) (odds ratio : 14.3, 95% CI, p < 0.001), and cerebral palsy/development disorders (OR: 12.7, 95% CI, p < 0.001), with similar estimates of VE in these subgroups as in the total cohort. In the VE analysis, there were 21 cases (0.004%) of COVID-19 hospitalisation among 2-dose recipients and 26 cases (0.016%) among controls, resulting in a VE of 76% (95% CI, p < 0.001). The safety analysis showed that vaccination was associated with 16% lower (95% confidence interval (CI), p < 0.001) risk of all-cause hospitalisation, and with marginal differences between the groups regarding the 30 selected diagnoses. Analyses were adjusted for age, sex, baseline date, and whether the individual was born in Sweden. The vaccine effectiveness (VE) against COVID-19 hospitalisation, and risk factors for hospitalisation, were evaluated in adolescents given 2 doses of monovalent mRNA vaccine ( N = 501,945), as compared to never vaccinated controls ( N = 157,979), for up to 5 months follow-up during an omicron predominant period (1 January 2022 to 5 June 2022). The outcomes included all-cause hospitalisation and 30 selected diagnoses until 5 June 2022. The safety analysis included all individuals in Sweden born between 20 (aged 11.3 to 19.2 years) given at least 1 dose of monovalent mRNA vaccine ( N = 645,355), and never vaccinated controls ( N = 186,918).

A cohort study was conducted using Swedish nationwide registers.

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