Eligibility criteria
| Inclusion criteria | Exclusion criteria | |
| Population | General population infected with COVID-19 (both sexes, all ages). | Special populations such as studying only cancer patients or persons with diabetes. |
| Exposure | Age, in years. | All other exposures that do not include age. |
| Comparator/control | Age reference, in years. | |
| Outcomes | Due to infection with COVID-19: risk of hospitalisation, admission to ICU, intubation and death. Risks measured as HRs, risk ratios and ORs. | Other outcomes, including outcomes of composite disease severity. |
| Study design | Cross-sectional, case–control and cohort studies. | Randomized Controlled Trials (RCTs), qualitative studies, ecological studies, case reports, experiments, congress abstracts and posters. |
Excluded are studies only reporting univariate (unadjusted) effect values of age.
Excluded are studies in which the age effect is not adjusted at least for three comorbidities listed here: diabetes mellitus, cardiovascular disease, cancer or immunodeficiency, chronic kidney disease, chronic liver disease and chronic pulmonary disease.
ICU, intensive care unit.