Medical Risk Classification For Severe COVID-19 Based On Chronic Medical Conditions: A Comparative Analysis

Background The European Centre for Disease Prevention and Control lists medical conditions conferring high- or moderate-risk for severe COVID-19. Individual European countries also developed risk classifications to guide COVID-19 vaccination recommendations. Objectives To examine discordance between national and European risk classifications for severe COVID-19 in the Netherlands and Norway across general, hospitalized, and deceased populations, and investigate related factors. Methods This multi-country data-linkage study included 17.4 million inhabitants in the Netherlands and 5.6 million in Norway in 2020. Medical conditions were defined using ICD-10 codes in the European and Dutch classifications, and ICD-10 and ICPC-2 codes in the Norwegian classification. Individuals were classified as high-, moderate-, or low-risk per each classification. Performance was evaluated using sensitivity, specificity, positive and negative predictive values (PPV, NPV), Brier score, and area under the curve (AUC). Results Discordance between classifications was 12–14% in the general population and 36-47% among hospitalized or deceased individuals. The European classification assigned more individuals to high-risk, while national classifications assigned more as moderate-risk. National classifications demonstrated higher sensitivity, particularly in Norway, while the European classification showed higher specificity. PPVs were ≤0.9% and NPVs near 100% across all classifications. Norway’s national classification had better discrimination and calibration, while in the Netherlands, the European classification better predicted mortality. Discordances frequently involved subjects with cardiovascular disease, lung disease, and diabetes. Conclusion The European classification defines a substantially broader high-risk population compared to national classifications. No single classification is universally optimal. Further research should refine which chronic conditions best predict severe COVID-19. Funding ZonMw, EU, FCT, Norwegian Research Council’s COVID-19 Emergency Call, iAPOGEE.