ABSTRACT
Background: The impact of coronavirus disease 2019 caused by Severe Acute Respiratory Syndrome Coronavirus 2 on hosts of Long Term Care Facilities (LTCFs) has been dramatic at global scale as aging and comorbitities pose individuals at increased risk of severe disease and death. Methods: Aim of this study was to evaluate SARS-CoV-2 S-IgG antibodies titers in 478 residents and 649 health care workers of the largest Italian nurse facility two months after the complete vaccination with BNT162B2. Associations among host-related factors and predictors of humoral response were investigated. Results: By stratifying levels of humoral responses, we found that 62.1%, 21.6%, 12.1% and 4.2% of hosts has high (>1,000 BAU/ml), medium (101-1,000), low (1-100) and null (<1 BAU/mL) S-IgG titers, respectively. Hosts with previous COVID-19 and those with SARS-CoV-2 N-IgG positive serology showed higher level of serological response (p<0.001 and p<0.001, respectively), while the administration of corticosteroid or cancer diminished all levels of specific antibodies (p=0.019 and p=0.004). Significant associations were observed for these parameters in those with suboptimal response (p<0.001, p<0.001, p=0.028 and p=0.005) and with a null one (p=0.005, p<0.001 and p=0.039). Predictors of an increased risk of null response were advanced age, corticosteroid therapy and diabetes mellitus (p=0.025, p=0.017 and p=0.037). In contrast, previous diagnosis of COVID-19 resulted strongly associated with a reduced risk of null response to vaccination (p<0.001). Conclusions: SARS-CoV-2 specific antibodies in elderly individuals need to be measured to consider a third dose of vaccine after mass vaccination for prevention of reinfections in LTCFs despite the maintenance of barrier measures.