The isolated effect of age on the risk of COVID-19 severe outcomes: a systematic review with meta-analysis

Romero Starke, K.; Reissig, D.; Petereit-Haack, G.; Schmauder, S.; Nienhaus, A.; Seidler, A.

Introduction Increased age has been reported to be a factor for COVID-19 severe outcomes. However, many studies do not consider the age-dependency of comorbidities, which influence the course of disease. Protection strategies often target individuals after a certain age, which may not necessarily be evidence-based. The aim of this review was to quantify the isolated effect of age on hospitalization, admission to ICU, mechanical ventilation, and death. Methods This review was based on an umbrella review, in which Pubmed, Embase, and pre-print databases were searched on December 10, 2020 for relevant reviews on COVID-19 disease severity. Two independent reviewers evaluated the primary studies using predefined inclusion and exclusion criteria. The results were extracted, and each study was assessed for risk of bias. The isolated effect of age was estimated by meta-analysis, and the quality of evidence was assessed using GRADE. Results Seventy studies met our inclusion criteria (case mortality n=14, in-hospital mortality n=44, hospitalization n=16, admission to ICU n=12, mechanical ventilation n=7). The risk of in-hospital and case mortality increased per age year by 5.7% and 7.4%, respectively (Effect Size (ES) in-hospital mortality=1.057, 95% CI:1.038-1.054; ES case mortality= 1.074, 95% CI:1.061-1.087), while the risk of hospitalization increased by 3.4% per age year (ES=1.034, 95% CI:1.021-1.048). No increased risk was observed for ICU admission and intubation by age year. There was no evidence of a specific age threshold at which the risk accelerates considerably. The confidence of evidence was high for mortality and hospitalization. Conclusions Our results show a best-possible quantification of the increase in COVID-19 disease severity due to age. Rather than implementing age thresholds, prevention programs should consider the continuous increase in risk. There is a need for continuous, high-quality research and living reviews to evaluate the evidence throughout the pandemic, as results may change due to varying circumstances.