ABSTRACT
The time course of antibodies against SARS-CoV-2 is not yet well elucidated, especially in people who underwent a vaccination campaign. In this study, we measured the antibodies anti-S1 and anti-RBD with two different methods, both in patients and in vaccinated subjects. One hundred and eight specimens from 48 patients with COVID-19 (time from the onset of symptoms from 3 to 368 days) and 60 specimens from 20 vaccinated subjects (collected after 14 days from the first dose, 14 days and 3 months after a second dose of Comirnaty) were evaluated. We used an ELISA method that measured IgG against anti-Spike 1, and a chemiluminescence immunoassay that measured IgG anti-RBD. In the patients, the antibodies concentrations tended to decline after a few months, with both the methods, but they persisted relatively high up to nearly a year after the symptoms. In the vaccinated subjects, the antibodies were already detectable after the first dose, but after the booster, they showed a significant increase. However, the decrease was rapid, given that 3 months after the second vaccination, they were reduced to less than a quarter. The conversion of the results into BAU units improves the relationship between the two methods. However, in the vaccinated subjects, there was no evidence of proportional error after the conversion, while in the patients, the difference between the two methods remained significant.
ABSTRACT
INTRODUCTION: The persistence of circulating antibodies to SARS-CoV-2 infection is not yet well known. We compare the results of 2 automated systems for the determination of IgG against SARS CoV-2 and assess the time-course of the IgG response. METHODS: IgG were measured in 103 specimens of 55 patients with COVID-19 (time from the symptoms' onset: 3-187 days) using the automated tests "Abbott SARS-COV-2 IgG" and "MAGLUMI 2019-nCoV IgG". RESULTS: The 2 methods had a concordance of 90.3%, but the quantitative correlation, although significant, showed dispersed results. All the specimens resulted positive after 17 days. However, the median concentrations of IgG rapidly increased up to 20 days and decreased for Maglumi IgG while Abbott IgG showed a constant trend up to 85 days, and then slowly declined. CONCLUSIONS: The titer of IgG against SARS-CoV-2 may significantly and rapidly decrease, but with a very different time-course depending on the method used for the determination.