Background: Severe asthma increases the risk of severe COVID-19 outcomes such as hospitalization and death. However, more studies are needed to understand the association between asthma and severe COVID-19.

Methods: A cohort of 150,430 adult asthma patients were identified in the Swedish National Airway Register (SNAR) from 2013 to December 2020. Data on body mass index, smoking habits, lung function, and asthma control test (ACT) were obtained from SNAR, and uncontrolled asthma was defined as ACT ⩽19. Patients with severe COVID-19 were identified following hospitalization or in death certificates based on ICD-10 codes U07.1 and U07.2. The Swedish Prescribed Drug register was used to identify comorbidities and data from Statistics Sweden for educational level. Multivariate logistic regression analyses were used to estimate associations with severe COVID-19.

Results: Severe COVID-19 was identified in 1067 patients (0.7%). Older age (OR = 1.04, 95% CI = 1.03–1.04), male sex (1.42, 1.25–1.61), overweight (1.56, 1.27–1.91), obesity (2.12, 1.73–2.60), high-dose inhaled corticosteroids in combination with long-acting β-agonists (1.40, 1.22–1.60), dispensed oral corticosteroids ⩾2 (1.48, 1.25–1.75), uncontrolled asthma (1.64, 1.35–2.00), cardiovascular disease (1.20, 1.03–1.40), depression (1.47, 1.28–1.68), and diabetes (1.52, 1.29–1.78) were associated with severe COVID-19, while current smoking was inversely associated (0.63, 0.47–0.85). When comparing patients who died from COVID-19 with those discharged alive from hospital until 31 December 2020, older age, male sex, and current smoking were associated with COVID-19 death.

Conclusion: Patients with uncontrolled asthma and high disease burden, including increased asthma medication intensity, should be identified as risk patients for severe COVID-19. Furthermore, current smoking is strongly associated with COVID-19 death in asthma.