Accuracy of the Canadian COVID-19 Mortality Score (CCMS) to predict in-hospital mortality among vaccinated and unvaccinated patients infected with Omicron: a cohort study

Objective The objective is to externally validate and assess the opportunity to update the Canadian COVID-19 Mortality Score (CCMS) to predict in-hospital mortality among consecutive non-palliative COVID-19 patients infected with Omicron subvariants at a time when vaccinations were widespread.Design This observational study validated the CCMS in an external cohort at a time when Omicron variants were dominant. We assessed the potential to update the rule and improve its performance by recalibrating and adding vaccination status in a subset of patients from provinces with access to vaccination data and created the adjusted CCMS (CCMSadj). We followed discharged patients for 30 days after their index emergency department visit or for their entire hospital stay if admitted.Setting External validation cohort for CCMS: 36 hospitals participating in the Canadian COVID-19 Emergency Department Rapid Response Network (CCEDRRN). Update cohort for CCMSadj: 14 hospitals in CCEDRRN in provinces with vaccination data.Participants Consecutive non-palliative COVID-19 patients presenting to emergency departments.Main outcome measures In-hospital mortality.Results Of 39 682 eligible patients, 1654 (4.2%) patients died. The CCMS included age, sex, residence type, arrival mode, chest pain, severe liver disease, respiratory rate and level of respiratory support and predicted in-hospital mortality with an area under the curve (AUC) of 0.88 (95% CI 0.87 to 0.88) in external validation. Updating the rule by recalibrating and adding vaccination status to create the CCMSadj changed the weights for age, respiratory status and homelessness, but only marginally improved its performance, while vaccination status did not. The CCMSadj had an AUC of 0.91 (95% CI 0.89 to 0.92) in validation. CCMSadj scores of 15 had observed mortality of >56.8%.Conclusions The CCMS remained highly accurate in predicting mortality from Omicron and improved marginally through recalibration. Adding vaccination status did not improve the performance. The CCMS can be used to inform patient prognosis, goals of care conversations and guide clinical decision-making for emergency department patients with COVID-19.