Brian K Kirui,1 Ailiana Santosa,1 Huiqi Li,1 Lowie EGW Vanfleteren,2,3 Caroline Stridsman,4 Fredrik Nyberg1 1School of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; 2COPD Center, Department of Respiratory Medicine and Allergology, Sahlgrenska University Hospital, Gothenburg, Sweden; 3Department of Internal Medicine and Clinical Nutrition, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; 4Department of Public Health and Clinical Medicine/The OLIN-Unit, Umeå University, Umeå, SwedenCorrespondence: Brian K Kirui, School of Public Health and Community Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Box 463, 405 30, Gothenburg, Sweden, Email brian.kirui@gu.seIntroduction: Assessing COVID-19 risk in asthma patients is challenging due to disease heterogeneity and complexity. We hypothesized that potential risk factors for COVID-19 may differ among asthma age groups, hindering important insights when studied together.Methods: We included a population-based cohort of asthma patients from the Swedish National Airway Register (SNAR) and linked to data from several national health registers. COVID-19 outcomes included infection, hospitalization, and death from Jan 2020 until Feb 2021. Asthma patients were grouped by ages 12– 17, 18– 39, 40– 64, and ≥ 65 years. Characteristics of asthma patients with different COVID-19 outcomes were compared with those in their age-corresponding respective source population.Results: Among 201,140 asthma patients studied, 11.2% were aged 12– 17 years, 26.4% 18– 39, 37.6% 40– 64, and 24.9% ≥ 65 years. We observed 18,048 (9.0%) COVID-19 infections, 2172 (1.1%) hospitalizations, and 336 (0.2%) COVID-19 deaths. Deaths occurred only among patients aged ≥ 40. When comparing COVID-19 cases to source asthma populations by age, large differences in potential risk factors emerged, mostly for COVID-19 hospitalizations and deaths. For ages 12– 17, these included education, employment, autoimmune, psychiatric, and depressive conditions, and use of short-acting β-agonists (SABA) and inhaled corticosteroids (ICS). In the 18– 39 age group, largest differences were for age, marital status, respiratory failure, anxiety, and body mass index. Ages 40– 64 displayed notable differences for sex, birth region, cancer, oral corticosteroids, antihistamines, and smoking. For those aged ≥ 65, largest differences were observed for cardiovascular comorbidities, type 1 diabetes, chronic obstructive pulmonary disease, allergic conditions, and specific asthma treatments (ICS-SABA, ICS-long-acting bronchodilators (LABA)). Asthma control and lung function were important across all age groups.Conclusion: We identify distinct differences in COVID-19-related risk factors among asthma patients of different ages. This information is essential for assessing COVID-19 risk in asthma patients and for tailoring patient care and public health strategies accordingly.Plain language summary: Why was the study done?Asthma patients may be more susceptible to COVID-19 outcomes. Asthma affects all ages, and COVID-19-related risk factors may vary with age. Investigating factors that contribute to COVID-19 infection, hospitalization, and mortality within distinct age groups of asthma patients can yield a more comprehensive understanding of the age-specific nuances of COVID-19 risk.What did the researchers do and find?We analyzed sociodemographic characteristics, comorbidities, prescribed medications, and clinical characteristics of asthma patients with COVID-19 in different age groups and compared them with their age-corresponding source asthma populations.Potential risk factors for COVID-19 and its outcomes differed by age group For ages 12-17, these included education, employment, autoimmune, psychiatric, and depressive conditions, and use of short-acting β-agonists (SABA) and inhaled corticosteroids (ICS). In the 18-39 age group, largest differences were for age, marital status, respiratory failure, anxiety, and body mass index. Ages 40-64 displayed notable differences for sex, birth region, cancer, oral corticosteroids, antihistamines, and smoking. For those aged ≥ 65, largest differences were observed for cardiovascular comorbidities, type 1 diabetes, chronic obstructive pulmonary disease, allergic asthma, and specific asthma treatments (ICS-SABA, ICS-long-acting bronchodilators (LABA)). Asthma control and lung function were important across all age groups.What do these results mean?These results emphasize the importance of recognizing age-specific patterns contributing to COVID-19 risk for consideration in causal analyses. The findings also highlight the necessity for age-specific approaches in both clinical and public health interventions in managing COVID-19 in asthma patients.Keywords: asthma, COVID-19, population-based, register-study, risk factors