Recovery of lung function during the first year after COVID-19: a systematic review and meta-analysis

Background Several studies have reported lung function impairment following COVID-19. Less is known about the subsequent recovery. Research question What is the recovery in lung function after COVID-19 during the first year after infection? Methods We conducted a systematic review and meta-analysis of studies that monitored individuals’ lung function from the time of infection to at least 1 year after infection. Primary outcomes were change in percent predicted forced expiratory volumes in 1 s (FEV₁), forced vital capacity (FVC) and diffusing capacity for carbon monoxide (D_LCO). Mean differences (MDs) with 95% confidence intervals were estimated using a random effects model. Results We included 23 studies (n=3347 participants). 20 (86.9%) studies had their first follow-up 3 months after infection and 21 (91.3%) had their second follow-up 12 months after infection. The MDs between the second and first follow-up visits of FEV₁, FVC and D_LCO were 3.1% (95% CI 1.8–4.5; p<0.01), 4.4% (95% CI 2.7–6.0; p<0.01) and 6.6% (95% CI 4.4–8.9; p<0.01), respectively. Recovery of FEV₁, FVC and D_LCO was greater in mechanically ventilated patients compared to individuals with less severe disease. Current smoking status, pre-existing chronic lung disease and age did not impact recovery during the first year after infection. Interpretation Recovery in lung function was evident during the first year after COVID-19, with the largest improvement in patients with the most severe infection. Further follow-up and large-scale studies are warranted to establish recovery trajectories of COVID-19 and other respiratory infections to identify patient subgroups needing additional follow-up to ascertain modifiable factors influencing pulmonary recovery.