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The findings in this memo are based on rapid searches in PubMed and Embase, as well as manual searches on websites of health authorities in selected countries. Two researchers shared tasks related to study selection and synthesis of results. In the current situation, there is an urgent need for identifying the most important evidence quickly. Hence, we opted for this rapid approach despite an inherent risk of overlooking key evidence or making misguided judgements.
Association between age and disease severity
Children are more mildly affected of covid-19 than adults. With increasing age, there seems to be an increasing proportion of covid-19 patients who need hospitalization and who will need intensive care. Reports from many countries clearly show that the risk of dying from COVID-19 is higher among the elderly.
Association between comorbidity and disease severity
The incidence of many diseases appears higher among patients who die of COVID-19 than among those who survive. However, as chronic diseases are more common among older people, it is difficult to determine whether the increased risk among the elderly is due to comorbidity, age, or a combination of these factors.
Age and/or comorbidity?
We identified three studies analysing multiple risk factors using multivariate models, but the results do not provide clear answers as to whether age or comorbidity is the most important risk factor for serious illness. It seems reasonable to view age as an independent risk factor for death from COVID-19, but the results for other risk factors are more uncertain. It is difficult to draw firm conclusions about the relative importance of the various risk factors as the available studies are small, with uncertain results. We expect that larger studies will soon be available, providing clearer answers about the relative importance of age and other risk factors for patients with COVID-19.