Impact of COVID-19 pandemic on asthma exacerbations: Retrospective cohort study of over 500,000 patients in a national English primary care database.

Background: Several countries reported a substantial reduction in asthma exacerbations associated with COVID-19 pandemic-related restrictions. However, it is not known if these early reported declines were short-term and if these have rebounded to pre-pandemic levels following easing of lockdown restrictions. Methods: We undertook a retrospective, cohort study of all asthma patients in a national primary care database of almost 10 million patients, Optimum Patient Care Database (OPCRD), identified from January 1, 2010, to December 31, 2015, using a previously validated algorithm. We subsequently followed the identified cohort of asthma patients from January 1, 2016, to October 3, 2021, and identified every asthma exacerbation episode with a validated algorithm. To quantify any pandemic-related change in exacerbations, we created a control time-series (mean of 2016-2019) and then compared the change in exacerbation rate in 2020-2021 over quarterly periods when compared with the control period (the pre-pandemic period). We undertook overall and stratified analyses by age group, sex, and English region. Findings: We identified 100,362 asthma patients (502,669 patient-years) from across England who experienced at least one exacerbation episode (298,390 exacerbation episodes during the entire follow-up). Except for the first quarter of 2020, the exacerbation rates were substantially lower (>25%) during all quarters in 2020-2021 when compared with the rates during 2016-2019 (39.7% (95% Confidence Interval (CI): 34.6, 44.9) in quarter-2, 2020; 46.5% (95%CI: 36.7, 56.4) in quarter-3, 2020; 56.3% (95%CI: 48.7, 63.9) in quarter-4, 2020; 63.2% (95%CI: 53.9, 72.5) in quarter-1, 2021; 57.7% (95%CI: 52.9, 62.4) in quarter-2, 2021; 53.3% (95%CI: 43.8, 62.8) in quarter-3, 2021). Interpretation: There was a substantial and persistent reduction in asthma exacerbations across England over the first 18 months after the first lockdown. This is unlikely to be adequately explained by changes in health-seeking behaviour, pandemic-related healthcare service disruption, or any air-quality improvements. Funding: Asthma UK, Health Data Research UK (HDR UK), Medical Research Council (MRC), National Institute for Health Research (NIHR).