Waves of inequality: Income differences in intensive care due to Covid-19 in Sweden

BACKGROUND: Individuals in lower social strata were overall more likely to develop severe Covid-19 during the pandemic. However, specific conditions in terms of preparedness, knowledge and the properties of the virus itself changed during the course of the pandemic. Socioeconomic inequalities in Covid-19 may therefore shift over time. This study examines the relationship between income and intensive care (ICU) episodes due to Covid-19 in Sweden during three distinct waves. METHODS: This study uses Swedish register data on the total adult population and estimate the relative risk (RR) of ICU episodes due to Covid-19 by income quartile for each month between March 2020 and May 2022, and for each wave, using Poisson regression analyses. RESULTS: The first wave had modest income-related inequalities, while the second wave had a clear income gradient, with the lowest income quartile having an increased risk compared to the high-income group (RR: 1·55 [1·36 - 1·77]). In the third wave, the overall need for ICU decreased, but relative risks increased, particularly the top and bottom income quartiles (RR: 3·72 [3·50 - 3·96]). Inequalities in the third wave were partly explained by differential vaccination coverage by income quartile, although substantial inequalities remained after adjustment for vaccination status (RR: 2·39 [2·20 - 2·59]). CONCLUSIONS: The study highlights the importance of considering the changing mechanisms that connect income and health during a novel pandemic. Health inequalities per income group increased for each subsequent wave. As the aetiology of Covid-19 became better understood those with more resources could better protect themselves from infection. Understanding the social dynamic of infectious diseases can help prepare for possible future pandemics. KEY MESSAGES: • Health inequalities in severe covid-19 infections increased as the pandemic progressed. • Understanding the social dynamic of infectious diseases can help prepare for possible future pandemics.