DYNAMICS OF ANTI-SPIKE PROTEIN IGG ANTIBODY LEVELS OVER A 10-MONTH PERIOD FOLLOWING VACCINATION OR INFECTION – A RETROSPECTIVE STUDY

"There is significant variation in antibody levels among patients exposed to SARS-CoV-2 or following vaccination. However, the quantity of antibodies at which one is considered protected, or for how long they can provide it, is unclear. In general, it is presumed that antibodies wane over time, more notably around the 6 months mark following the second dose. Our study aimed to observe these processes dynamically, by tracking the variation of IgG anti-Spike protein antibody levels in a population of volunteers at the Cantacuzino National Military Medical Institute for Research and Development. A total of 1338 samples from 524 participants, either symptomatic or asymptomatic, were collected before vaccination and at predetermined intervals after the first and second dose, over a 10-month period (December 2020 - October 2021). The samples were tested via enzyme-linked immunosorbent assay (ELISA) method, using commercial Anti-SARS-CoV-2 QuantiVac ELISA (IgG) quantitative test kits - Euroimmun (Medizinische Labordiagnostika). The majority of participants were vaccinated with BNT162b2 (Pfizer BioNTech) (474 participants – 90.46%). Samples were grouped according to the length of time between exposure (infection or vaccination) and testing, along with exposure type (vaccinated, vaccinated with prior infection, unvaccinated with prior infection). The data suggests that vaccinated participants, with or without a history of infection, held higher antibody levels compared to unvaccinated participants with a history of infection. A decline in antibody levels over time in all test groups was noted, though less steep among participants with a history of infection."