Long-Term Dynamic of Anti-TrimericS and Anti-RBD Antibodies in Naive and COVID-19 Recovered mRNA-1273 Vaccine Recipients

Objective Patients and physicians are increasingly requesting their clinical laboratory to provide SARS-CoV-2 serology interpretation. Our study aimed to assess the evolution of SARS-CoV-2 antibodies in Moderna-vaccinated health care workers. Methods We analyzed the evolution of mRNA-1273 (Moderna)-elicited antibodies by 2 high-throughput assays, TrimericS IgG (Diasorin) and SARS-CoV-2 IgG-II (Abbott). Results After the first injection, the COVID-19-recovered vaccinees showed a serological response as strong as that observed 1 month after the second injection in participants without COVID-19 history. Although remaining above the positivity thresholds, the TrimericS immunoglobulin G (IgG) and anti-RBD (receptor-binding domain) IgG levels fell considerably between 1 and 7 months postvaccination, dropping to 10.6% and 13% for the COVID-19 recovered subgroup and to 11.7% and 9.3% for the COVID-19 naive subgroup. Conclusion Regardless of the test used, a decrease in circulating anti-SARS-CoV-2 IgG levels should be expected a few months after vaccination. As this decline does not preclude the efficacy of immune response, caution is necessary when interpretating postvaccination serological data.