ABSTRACT
OBJECTIVES: Understanding immune response is critical for control of COVID-19 pandemic. However, recent studies show that vaccine-induced humoral immunity may not be long-lasting and weaker in SARS-CoV-2 variants of concern. METHODS: In May 2021, 253 self-nominated persons were tested for antibodies against SARS-CoV-2 in 1 to 104 days (mean 41, median 28) after two doses of Moderna and Pfizer-BioNTech vaccines in the city of Brno, Czechia. Two point-of-care iCHROMA™ II immunofluorescence assays were used: COVID-19 Ab against mix of SARS-CoV-2 nucleocapsid and spike proteins (IgG Ab); and COVID-19 nAb against S1-RBD protein (nAb). Results were analysed in relation to gender, age, vaccine, and past COVID-19 disease. RESULTS: Antibodies nAb were detectable in 92.9% (95% CI: 89.7-96.0) of vaccinees. We observed statistically insignificant decrease of positive results from 93.9% (95% CI: 89.5-98.3) and 97.0% (95% CI: 92.8-100.0) in the first and second month after vaccination, respectively, to 91.7% (95% CI: 83.8-99.5) and 78.3% (95% CI: 61.4-95.1) in the third and fourth month, respectively. Quantitative results showed decreasing level of nAb in both genders, age groups and vaccines. Higher levels of nAb were found in younger age group and in COVID-19 convalescents. IgG Ab showed little dynamics in time. CONCLUSIONS: We found robust humoral response after vaccination with mRNA vaccines, however, decreasing nAb levels suggest that vaccine-induced humoral immunity is rapidly waning. This finding is relevant for adjustment of vaccination strategies with regard to inclusion of booster dose(s).