Tracking antibody dynamics in COVID-19 recovered patients: A longitudinal study at tertiary care hospital in Lahore

Objective: To determine the persistence of SARS-CoV-2 IgG antibodies in COVID-19 recovered patients 9 months after recovery. Material and Methods: It is a longitudinal cohort study which was conducted at Pathology department, tertiary care hospital Lahore. Regardless of age or gender, we measured Anti-SARS-CoV-2 IgG against SARS-COV-2 spike antigen in 250 COVID-19 recovered patients at three distinct time-lines (150-170, 171-220, and 221-270 days) respectively. Those who had reinfection (MA2) or had received vaccination during this time were not included in the study. Semi-quantitative Enzyme Linked Immuno-Sorbent Assay (ELISA) was used to measure the antibodies. Antibody ratio levels of less than 0.8 were regarded as negative, those between 0.8 and 1.1 as borderline, and those greater than 1.1 as positive. Results: Out of total 250 patients, 88% (220) of the patients were male while 12% (30) were female. Minimum age of study participants was 9 yrs and maximum age was 65 yrs. Mean age of patients was 35 yrs. We found that 151 (68%) of the male study participants and 19 (63%) of the female participants were seropositive at 150 days after COVID-19, whereas 66 (30%) of the male participants and 11 (37%) of female participants were seropositive at 270 days after COVID-19. The percentage of male seropositivity has decreased by 56%, whereas the percentage of female seropositivity has decreased by 41%. Conclusion: This study has demonstrated that the serological IgG immune response against SARS-CoV-2 showed a diminishing trend after nine months. Keywords: COVID-19, ELISA, IgG antibodies, SARS-CoV-2