Impact of interstitial lung disease on COVID-19 severity: A nationwide register study

Aim: To investigate if ILD is associated with increased severity of COVID-19 and if this association differs by disease type or vaccination status. Methods: Data from Swedish national registers within the SCIFI-PEARL study was used to examine the relationship between ILD and three levels of COVID-19 severity: non-hospitalized, hospitalized, and critical (ICU admission or death) from January 2020 to May 2022. We performed multinomial logistic regression, adjusted for confounding factors, and examined interactions with vaccination status. Results: Altogether, 18,666 patients with ILD were included, comprising 8774 with fibrotic ILD and 9181 with sarcoidosis. Among ILD patients with COVID-19 (n = 3384), 18.9 % required hospitalization and 8.5 % had critical disease, compared to 3.8 % and 1.3 % respectively, among COVID-19 patients without ILD. ILD was associated with increased severity of COVID-19 compared to patients without ILD (Conditional Odds Ratio (COR) (95 % CI)): hospitalization 2.30 (2.09–2.54), critical disease 2.50 (2.17–2.88)). Corresponding CORs were 3.25 (2.81–3.75) and 3.46 (2.88–4.15) for fibrotic ILD, and 1.56 (1.34–1.81) and 1.57 (1.21–2.03) for sarcoidosis.Two or more vaccine doses protected against severe COVID-19 among patients with ILD and COVID-19, reducing hospitalizations (non-vaccinated: 21.8 %; vaccinated: 16.3 %), and an even stronger reduction in critical disease (non-vaccinated: 12.0 %; vaccinated: 3.6). However, even among fully vaccinated individuals, ILD remained significantly associated with increased severity of COVID-19. Conclusions: ILD is associated with increased COVID-19 severity in patients with infection, particularly in patients with fibrotic ILD. Vaccination most effectively prevents critical illness. Our study underscores the continued importance of vaccination programs and preventive strategies.