Santos, João AlmeidaGaio, VâniaAmaral, PalmiraHenriques, CamilaGuiomar, RaquelMachado, Ausenda2026-06-162026-06-162024-09-24http://hdl.handle.net/10400.18/11331Objective: Healthcare workers (HCWs) have a higher risk of SARS-CoV-2 infection due to their direct contact with patients. On the other hand, they can also act as a source of in-hospital transmission. We assessed SARS-CoV-2 serological status of HCWs at a Portuguese central hospital before vaccination, three and six months after the 2023 COVID-19 booster vaccination program. Methods: We conducted a serological follow-up study among a cohort of HCWs from a Portuguese central hospital, with three rounds of testing: pre-COVID-19 vaccination (September/October 2023), three months (January/February 2024), and six months (April/May 2024) post-vaccination. During follow-up, only participants who underwent pre-vaccination serology and were vaccinated were included. SARS-CoV-2 spike receptor-binding domain (anti-RBD/S) protein-specific IgG antibodies were measured (upper limit of detection 40000 AU/mL). Descriptive statistics and Pearson Chi-Square test analysis were performed. Results: All participants (n=177, median age: 47 years, 77,4% females) had the complete primary COVID-19 vaccination with 78,0% having received 2 additional booster doses prior to 2023 vaccination program. At pre-vaccination, all HCWs had anti-RBD/S IgG antibodies with 11,9% (n=21) presenting a concentration >40000 AU/mL. Three months later, 35,0% HCWs (n=62) underwent retesting, with 40,3% presenting anti-RBD/S IgG antibody concentrations >40000 AU/mL. After six months, 26,6% HCWs (n=47) repeated testing, with 21,3% (n=10) having antibody concentrations >40000 AU/mL. The differences in anti-RBD/S IgG antibody concentrations between the three rounds of testing were significant. Conclusions: Three months post-COVID-19 2023 autumn vaccination, an increase in the concentration of anti-RBD/S antibodies was identified among HCW, but after six months this concentration decreased. These results are in line with the expected decay of antibodies over time after 3 months of vaccination and reinforce the importance of revaccination in HCWs.engSARS-CoV-2COVID-19Serological StatusVaccinesVEBISPublic HealthEstados de Saúde e de DoençaInfecções Respiratóriasconference object