Immune responses to SARS-CoV-2 infection and vaccine in a big Italian COVID-19 Hospital: an 18-month follow-up

Abstract

OBJECTIVES: This is a longitudinal prospective study designed to assess the trend of anti-SARS-CoV-2 antibodies targeting the Spike (anti-S) and Nucleocapside protein (anti-N) viral antigens over a 9-month period after the administration of anti-SARS-CoV-2 vaccine in a big COVID-19 hospital located in Northern Italy.  PARTICIPANTS: 7,411 vaccinated workers were included in a linear mixed effect model analysis performed to model the anti-S decay over the 9 months following the vaccination, during serological screening performed approximately 2, 4 and 9 months following the 1st jab administration. Serological tests performed in the 9 months preceding vaccine administration were retrospectively analysed to identify the burden of infections occurring before vaccination. RESULTS: The serological assays were used for monitoring the antibody titres during the observational period.  Vaccination significantly reduced the rate of infection and elicited a specific humoral response, which lasted during the whole observational period (9 months). A decay was observed in all considered subgroups. At 35 weeks, workers with no history of pre-vaccine infection showed a significantly lower anti-S titer [-2522 U/mL on average (-2589.7 to -2445.7)]; younger workers showed significantly higher anti-S titres [140.2 U/mL on average (82.4 to 201.3)]. Only 7 immunocompromised workers did not show significant levels of anti-S antibodies; three of them, all females, showed a specific T-cell response. CONCLUSIONS: Comparing the 9-months periods before and after the first vaccine dose, a significant reduction in infection rate was observed (1708 cases vs 156). Pre-vaccine infection, especially if contracted during the first pandemic wave greatly enhanced the response to vaccination, which was significantly affected also by age both in extent and duration (inversely related). A gender effect on the T-cell immune response was observed in a small group of workers who do not produce antibodies after vaccine administration. REGISTRATION: approved by the Ethics Committee of Brescia (ID#: NP 4589).