A longitudinal follow-up of COVID-19 patients in the convalescent phase showed recovery in radiological results, the dynamics of lymphocytes, and a decrease in the level of IgG antibody: a single-centre, observational study

BACKGROUND: Given the high prevalence of coronavirus disease 2019 (COVID-19) globally, and the increased number of patients being discharged, it is necessary to understand the health consequences of COVID-19 to formulate and manage public policy concerning convalescent patients. METHODS: A longitudinal follow-up investigation of 25 patients from a tertiary hospital in Henan provincial was conducted 8 weeks after discharge. Of these patients, 15 attended a second follow-up appointment 8 weeks after that. A throat swab reverse transcription-polymerase chain reaction (RT-PCR) analysis for SARS-CoV-2 and chest computerized tomography (CT) scans were implemented at the first follow-up appointment, and a total of 40 blood samples (25 from the first and 15 from the second follow-up appointment) were collected. Patients’ levels of Immunoglobulin G (IgG) antibody against S-Receptor binding domain (S-RBD) and Nucleocapsid Protein (NP) of SARS-CoV-2 and the subpopulation of lymphocytes were evaluated using an enzyme-linked immunoassay (ELISA) test and flow cytometry, respectively. RESULTS: At the first follow-up appointment, 10 of the 25 patients (40.0%) showed complete radiological resolution. Of these patients, 80.0% were classified as moderate, and 80.0% were younger (those whose age was ≤ the median age of all the patients). The predominant patterns of abnormalities included an irregular line (12/25, 48.0%), ground-glass opacity (GGO) (44.0%), and multiple GGOs (28.0%). At the first follow-up appointment, 40.0% (10/25) of patients still had lymphopenia. Of the 15 patients who were followed-up with twice, the ratio of lymphopenia was 80% (12/15), 60.0% (9/15), and 46.7% (7/15) at 0, 8, and 16 weeks after discharge, respectively. This was mainly due to a decrease in the cluster of differentiation (CD) 4+ T lymphocyte, which was observed in 60% (9/15), 60% (9/15), and 46.7% (7/15) of total patients at 0, 8, and 16 weeks after discharge, respectively. All of the patients were S-RBD and NP IgG antibody positive at the first follow-up appointment. 40.0% (6/15) and 66.7% (10/15) of patients showed a decrease over 50.0% in the level of NP and S-RBD IgG antibodies, respectively, at the second follow-up appointment. The NP and S-RBD IgG antibodies’ levels declined to 44.6% (P=0.044) and 28.1% (P=0.18), respectively. 0 and 26.7% (4/15) of patients turned from NP and S-RBD IgG antibody positive to negative, respectively. CONCLUSIONS: About half of the patients still showed at least 1 abnormality in chest CT scans 8 weeks after discharge and lymphopenia 16 weeks after discharge. The level of the IgG antibody had declined by the follow-up appointment. Notably, the S-RBD IgG antibody declined more dramatically than that of NP. These results may have implications in the making of policies related to disease prevention, the long-term management of discharged patients, and vaccines’ development.