Background: Marginalised or deprived groups may be at high risk of a serious COVID-19 outcome. We examined adverse outcomes associated with SARS-CoV-2 infection among vulnerable segments of society.

Methods: Using health and administrative registers, we performed a population-based cohort study of 4.38 million Danes, 27 February 2020­ to 6 April 2021. Main predictors were experiences of 1) homelessness, 2) imprisonment, 3) supported psychiatric housing, 4) mental disorder, 5) substance abuse, and 6) chronic medical condition. COVID-19-related outcomes were: 1) hospitalisation, 2) intensive care, 3) 30-day mortality, and 4) overall mortality. PCR-confirmed SARS-CoV-2 infection and PCR-testing were also studied. Vulnerable groups were compared with the general population (using adjusted incidence and mortality rate ratios: IRRs, MRRs).

Findings: Among individuals with a positive PCR-test experiencing homelessness and supported psychiatric housing, 8∙6% (95% CI 6∙9-10∙4) and 11% (7∙8-14∙7), respectively, were admitted to hospital within two weeks and 1∙8% (1∙1-2∙7) and 2∙9% (1∙4-5∙1), respectively, had died within 30 days. The probability of hospitalisation was higher for all predictors compared with the general population (p=<0∙0001). After adjustments, vulnerable housing situations, i.e. homelessness, imprisonment, and supported psychiatric housing, increased the risk of adverse outcomes 1∙7 to 3∙2-times; highest 30-day MRR after COVID-19 was for homelessness (3∙2, 95% CI 2∙0-5∙1) and supported psychiatric housing: (2∙7, 1∙4-5∙2). Mental disorder, substance abuse, and chronic medical conditions were associated with 1∙1 (mental disorder and intensive care, p=0∙37) to 2∙0-times increased risk of adverse outcomes (30-day MRR for substance abuse: 2∙0, 1∙8-2∙3). Overall mortality during the study period was increased for all predictors and highest for homelessness combined with a PCR-confirmed SARS-CoV-2 infection (MRR 22∙1, 15∙2-32∙2).

Interpretation: This study highlights that pandemic preparedness should address inequalities in health, including infection prevention and vaccination of vulnerable groups. Higher awareness of people in vulnerable living situations is needed.