Publication date: Jul 11, 2025

Coronavirus disease 2019 (COVID-19) is a highly contagious infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible for millions of deaths and substantial morbidity worldwide. Several studies report that up to 50% of individuals who recover from acute SARS-CoV-2 infection experience a plethora of long-COVID symptoms that may persist for weeks, months, or even up to a year. Abnormal pulmonary function is one of the most critical manifestations of long-COVID, even after recovering from COVID-19. Understanding the long-term pulmonary consequences and immune response among individuals recovering from COVID-19, who experienced disease severity ranging from mild to severe, is crucial for comprehensive post-recovery care and vaccination strategies. This prospective case-control study included 29 individuals who had recovered from COVID-19 with a history of mild to severe symptoms and 64 controls. Assessments of pulmonary functional measures, such as FVC, FEV1, FEV1/FVC ratio, FEF, MEF, and PEF were carried out following recovery from COVID-19. Additionally, IgG antibody responses were examined by ELISA for up to six months through multiple follow-ups following two doses of vaccination, with an additional follow-up 30 days after the booster dose (third dose). Pulmonary functional abnormalities were prevalent in the recovered group, which had previously exhibited varying symptom severity (53% mild, 66% moderate, and 50% severe) compared to the control group (23%). Higher IgG antibody titers were observed among the recovered group, with significantly elevated titers in severe and moderate cases following vaccination. After vaccination, the recovered group showed significantly higher titers at day 14, particularly in the severe (1418 IU/mL) and moderate (1390 IU/mL) groups, compared to the control group (968 IU/mL) (p 

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