Long-term outcomes in COVID-19 patients admitted to intensive care in Denmark: A nationwide observational study

Background Among ICU patients with COVID-19, it is largely unknown how the overall outcome and resource use have changed with time, different genetic variants, and vaccination status.Methods For all Danish ICU patients with COVID-19 from March 10, 2020 to March 31, 2022, we manually retrieved data on demographics, comorbidities, vaccination status, use of life support, length of stay, and vital status from medical records. We compared patients based on the period of admittance and vaccination status and described changes in epidemiology related to the Omicron variant.Results Among all 2167 ICU patients with COVID-19, 327 were admitted during the first (March 10-19, 2020), 1053 during the second (May 20, 2020 to June 30, 2021) and 787 during the third wave (July 1, 2021 to March 31, 2022). We observed changes over the three waves in age (median 72 vs. 68 vs. 65 years), use of invasive mechanical ventilation (81% vs. 58% vs. 51%), renal replacement therapy (26% vs. 13% vs. 12%), extracorporeal membrane oxygenation (7% vs. 3% vs. 2%), duration of invasive mechanical ventilation (median 13 vs. 13 vs. 9 days) and ICU length of stay (median 13 vs. 10 vs. 7 days). Despite these changes, 90-day mortality remained constant (36% vs. 35% vs. 33%). Vaccination rates among ICU patients were 42% as compared to 80% in society. Unvaccinated versus vaccinated patients were younger (median 57 vs. 73 years), had less comorbidity (50% vs. 78%), and had lower 90-day mortality (29% vs. 51%). Patient characteristics changed significantly after the Omicron variant became dominant including a decrease in the use of COVID-specific pharmacological agents from 95% to 69%.Conclusions In Danish ICUs, the use of life support declined, while mortality seemed unchanged throughout the three waves of COVID-19. Vaccination rates were lower among ICU patients than in society, but the selected group of vaccinated patients admitted to the ICU still had very severe disease courses. When the Omicron variant became dominant a lower fraction of SARS-CoV-2 positive patients received COVID treatment indicating other causes for ICU admission.