BACKGROUND While global health agencies have listed asthma as a vulnerability for severe cases of coronavirus disease 2019 (COVID-19), the evidence supporting this is scarce.

METHODS A nationwide cohort study was conducted using the validated Korean national health insurance claim data of patients diagnosed with COVID-19 between January 1 and April 8, 2020. Asthma comorbidity was determined using a diagnosis code assigned by the physician and the prescription of asthma-related medications. The clinical course of COVID-19 was classified into 3 severity grades according to the requirements for oxygen supply and mechanical ventilation. We also evaluated the association of asthma with overall and in-hospital mortality of COVID-19.

RESULTS Asthma morbidity was a significant risk factor for severe COVID-19 (grade 2 requiring oxygen supply) (adjusted odds ratio [aOR] = 1.341, 95% confidence interval [CI], 1.051-1.711, P = 0.018) and grade 3 requiring mechanical ventilation or leading to death (aOR = 1.723, 95% CI: 1.230-2.412, P = 0.002) multinomial logistic regression adjusting co-risk factors. Asthma was also significantly associated with mortality of COVID-19 (aOR = 1.453, 95% CI: 1.015-2.080, P = 0.041) and was revealed to have a shorter time to in-hospital mortality of COVID-19 (P < 0.001). Patients with recent asthma exacerbation showed more severe COVID-19 of grade 3 (OR = 7.371, 95% CI: 2.018-26.924, P = 0.003) and higher mortality (OR = 9.208, 95% CI: 2.597-32.646, P < 0.001) in univariable analysis, but the statistical significance was not found in multivariable analysis.

CONCLUSION Asthma morbidity was associated with severity and mortality of COVID-19. Patients with asthma should pay more attention to avoid worsening of COVID-19.