Pulmonary function and comparative SARS-CoV-2 RBD-specific IgG antibody response among the COVID-19 recovered group

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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 experienced a plethora of long-COVID symptoms 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 symptoms, 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 who previously exhibited different symptoms (53% mild, 66% moderate, and 50% severe) compared to the control group (23%). Higher IgG antibody titers were observed among the recovered groups, significantly elevated in severe and moderate cases following vaccination. Following vaccination, the recovered group who experienced disease history showed significantly higher titers at day 14, particularly in severe (1418 IU/mL) and moderate (1390 IU/mL) groups compared to the control group (968 IU/mL) (p<0.005). Notably, antibody titers are negatively correlated with pulmonary function test (PFT) parameters such as Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1 second (FEV1). All groups experienced a significant (p<0.005) decrease in antibody titers within 90-120 days of two doses of vaccination. After five to six months, the titers were comparable to the baseline titer, indicating the importance of vaccination and booster doses regardless of previous infection history. Overall, our study underscores the significance of pulmonary function assessment post-COVID-19 recovery for long-term respiratory health and emphasizes the importance of vaccination regardless of infectious history. To ensure long-term respiratory health, this study emphasizes the significance of evaluating pulmonary function in those who might have contained asymptomatic COVID-19 infections as well as those who have recovered from symptomatic COVID-19 infections. Furthermore, these findings underscore the importance of vaccination regardless of infection history as a key strategy in pandemic preparedness. To assess the impact of long-COVID on respiratory health, this study underscores the importance of evaluating pulmonary function in individuals, whether they had symptomatic or asymptomatic COVID-19. Furthermore, the findings from the immune response analysis highlight the critical role of vaccination, regardless of infection history, as a key strategy of pandemic preparedness.