Clinical characteristics and outcomes of critically ill patients with one, two and three doses of vaccination against COVID‐19 in Australia

Background Vaccination has been shown to be highly effective in preventing death and severe disease from severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection. Currently, few studies have directly compared vaccinated and unvaccinated patients with severe COVID‐19 in the intensive care unit (ICU). Aims To compare the clinical characteristics and outcomes of vaccine recipients and unvaccinated patients with SARS‐CoV‐2 infection admitted to the ICU in a nationwide setting. Methods Data were extracted from the Short PeRiod IncideNce sTudy of Severe Acute Respiratory Infection Australia, in 57 ICU during Delta and Omicron predominant periods of the COVID‐19 pandemic. The primary outcome was inhospital mortality. Secondary outcomes included duration of mechanical ventilation, ICU length of stay, hospital length of stay and ICU mortality. Results There were 2970 patients admitted to ICU across participating sites from 26 June 2021 to 8 February 2022; 1134 (38.2%) patients were vaccine recipients, and 1836 (61.8%) patients were unvaccinated. Vaccine recipients were older, more comorbid and less likely to require organ support. Unadjusted inhospital mortality was greater in the vaccinated cohort. After adjusting for age, gender and comorbid status, no statistically significant association between inhospital or ICU mortality, and vaccination status, was apparent. Conclusion We found COVID‐19 infection can cause severe disease and death in vaccine recipients, though comorbid status and older age were significant contributors to mortality. Organ support requirements and the number of deaths were highest in the unvaccinated cohort.