Background Longitudinal assessment and reversibility of changes in the pulmonary function tests in the post-acute phase of COVID-19 across the whole spectrum of severity of infection is needed to understand the long-term burden of the disease. Methods This was a prospective cohort of symptomatic patients with a positive SARS-CoV-2 (molecular or antigenic) test. Participants were divided based on infection severity at baseline as mildly-ill (B1), moderately-ill (B2), severely-ill (B3), critically-ill (B4) (Fig.1). Follow-up consisted of 4 visits: within 7 days from discharge (BL), and at months 1 (M1), 3 (M3), and 6(M6). We report findings up to M3 for participants enrolled August 2021- March 2022. Pulmonary function capacity was assessed with carbon monoxide diffusing capacity (DLCO), spirometry, and 6-minute walk test (6MWT). A DLCO< 80% was considered abnormal and reverted if >80% at follow-up visits. Study population divided by severity of infection Results Out of 206 eligible participants, 110 were enrolled, of which 96 (87%%), 79 (72%), and 52(47.2%) were evaluated at BL, M1, and M3, respectively (Fig.2). Most (67%) participants were male, median age was 37.5 years old (IQR: 28-46.3) and median body mass index was 26.7 (IQR:23.7-30.4). Regarding severity, 39 (41%) participants were classified as critically-ill (B4) at BL. No underlying comorbidities were reported among 63 (66%) participants, while diabetes type 2 (11%), asthma (7%) prior pulmonary tuberculosis (6%) and hypertension (5%) where the most frequent comorbidities overall; 17 (18%) reported smoking exposure. There were significant differences accross severity groups for sex, age, absence of comorbidities, and dyspnea during the acute phase of COVID-19 (Tab.1). At Of the 88 (92%) participants that underwent the pulmonary function tests at BL: 49 (56%) had DLCO < 80% with a tendency to revert across B1-B4 groups at month 3 (Fig.3). Spirometry parameters (Forced Vital Capacity, Forced Expiratory Volume 1, Peak Expiratory Flow) and distance walked on 6MWT were different across groups. Flowchart of the study population Demographics of study population stratified by groups of severity Median DLCO adjusted for hemoglobin value at baseline, month 1 and month 3 visits stratified by groups of severity of infection. Conclusion Abnormal DLCO tended to increase and revert to values greater than 80% in the 3-month follow-up period of patients recovered from SARS-CoV-2 infection across severity groups. Disclosures All Authors: No reported disclosures.