Background: Social distancing measures introduced during the COVID-19 pandemic may have an effect on non-COVID-19 admissions for severe acute exacerbation of chronic obstructive pulmonary disease (s-AECOPD). Our aim was to determine the risk of s-AECOPD prior to and after the social distancing period was implemented in Denmark on March 12, 2020.

Methods: A nationwide observational cohort study comparing data from all Danish inhabitants between calendar week 1 through 25 in 2019 and 2020, extracted from Danish health registries. A sub-study of s-AECOPD, all-cause mortality, and admissions to intensive care unit (ICU) in outpatients with specialist confirmed diagnosis of COPD was conducted for the same calendar periods.

Results: A total of 3.0 million inhabitants aged 40+ years, corresponding to 3.0 million person-years, were followed for s-AECOPD. In the social distancing period in 2020, there were 6,212 incidents of s-AECOPD as compared to 11,260 incidents of s-AECOPD in the same time period in 2019, which corresponds to a relative risk reduction of 45%. In the COPD outpatient cohort (N=16,675), we observed a lower risk of s-AECOPD with the social distancing period (hazard ratio [HR] 0.34, 95%-confidence interval [CI] 0.33-0.36, p<0.001, absolute risk: 25.4% in 2020 and 42.8% in 2019, number needed to treat=6). The risk of all-cause mortality was reduced (HR 0.83, CI 0.76-0.90, p=0.004) as was ICU admissions (HR 0.63, CI 0.47-0.87, p=0.004).

Conclusions: The social distancing period was associated with a risk reduction for hospital admittance with s-AECOPD of a larger magnitude than any other known intervention.