Antibody responses to BNT162b2 SARS‐CoV‐2 mRNA vaccine among healthcare workers and residents of long‐term care facilities: A cohort study in Northern Italy

Background and Aims Long‐term care facilities (LTCFs) have been severely impacted by COVID‐19, with a disproportionate amount of SARS‐CoV‐2 infections and related deaths occurring among residents. Methods This study is part of an ongoing multicenter, prospective cohort study conducted among healthcare workers (HCWs) and residents of 13 LTCFs in Northern Italy designed to evaluate SARS‐CoV‐2 specific immunoglobulin class G (IgG) titers before and following vaccination with Pfizer/BNT162b2 SARS‐CoV‐2 mRNA vaccine (two doses of vaccine, 21 days apart). Serum samples were obtained from participants (t0) before vaccination, and (t1) 2 weeks after and analyzed to determine anti‐S1 IgG antibodies. Results Five hundred and thirty‐four participants were enrolled (404 subjects participated in both blood draws). Seropositivity was 50.19% at t0 and 99% at t1, with a significant difference in IgG titers. A higher proportion of residents were seropositive at t0 compared with HCWs, with significantly higher IgG titers among residents at both t0 and t1. Pre‐existing immunity also had a significant effect on postvaccination IgG titers. However, a significant difference in titers at t1 between HCWs and residents considering only participants seropositive at t0 was found, with higher median titers among previously seropositive residents. Conclusion Findings of this study provide scientific evidence endorsing the policy of universal vaccination in LTCFs.

Antibody responses to BNT162b2 SARS-CoV-2 mRNA vaccine among healthcare workers and residents of long-term care facilities: A cohort study in Northern Italy.

Background and Aims: Long-term care facilities (LTCFs) have been severely impacted by COVID-19, with a disproportionate amount of SARS-CoV-2 infections and related deaths occurring among residents. Methods: This study is part of an ongoing multicenter, prospective cohort study conducted among healthcare workers (HCWs) and residents of 13 LTCFs in Northern Italy designed to evaluate SARS-CoV-2 specific immunoglobulin class G (IgG) titers before and following vaccination with Pfizer/BNT162b2 SARS-CoV-2 mRNA vaccine (two doses of vaccine, 21 days apart). Serum samples were obtained from participants (t0) before vaccination, and (t1) 2 weeks after and analyzed to determine anti-S1 IgG antibodies. Results: Five hundred and thirty-four participants were enrolled (404 subjects participated in both blood draws). Seropositivity was 50.19% at t0 and 99% at t1, with a significant difference in IgG titers. A higher proportion of residents were seropositive at t0 compared with HCWs, with significantly higher IgG titers among residents at both t0 and t1. Pre-existing immunity also had a significant effect on postvaccination IgG titers. However, a significant difference in titers at t1 between HCWs and residents considering only participants seropositive at t0 was found, with higher median titers among previously seropositive residents. Conclusion: Findings of this study provide scientific evidence endorsing the policy of universal vaccination in LTCFs.

Serological Responses up to 9 Months following COVID-19 mRNA Vaccination in Residents and Health-Care Workers of Long-Term Care Facilities: A Multicenter Prospective Cohort Study in Northern Italy.

Long-term care facilities (LTCFs) were severely affected by COVID-19, in particular in Northern Italy. We aimed to assess antibody responses among residents and healthcare workers (HCWs) of 13 LTCFs through serum samples collected at three time points: prior to, two weeks, and 9 months after receiving Pfizer/BNT162b2 SARS-CoV-2 mRNA vaccine (respectively t0, t1, and t2). IgG antibodies targeted towards the S1 domain of the spike protein were measured, and results were expressed in binding antibody units (BAU/mL). Friedman's average rank test was performed to compare antibody titres between the three time points. Two logistic regression models were built to identify independent predictors of (1) developing and (2) maintaining a significant antibody response to vaccination, using a previously identified threshold. In total, 534 subjects were enrolled (371 HCWs and 163 residents). The antibody titres at t1 were the highest; at t2, the IgG titres significantly decreased, remaining however 10 times higher compared to titres at t0. Previous infection was the only significant predictor of developing and maintaining a response over threshold in both models. Results of this study provided further insights on the humoral response elicited by vaccination, and on host factors determining variations in its magnitude and kinetics.

Seroprevalence of infection-induced SARS-CoV-2 antibodies among health care users of Northern Italy: results from two serosurveys (October-November 2019 and September-October 2021).

OBJECTIVES: The objective was to estimate the seroprevalence of SARS-CoV-2 in autumn 2019 (before case zero was identified in Italy) and 2021 among residual sera samples from health care users in the Piedmont region of northwestern Italy. METHODS: Two serosurveys were conducted. Using a semiquantitative method, samples were tested for the presence of immunoglobulin G (IgG) antibodies against the S1 domain of the spike protein. Samples with positive test results from the 2019 survey were independently retested using a multiplex panel to detect IgG antibodies against the receptor binding domain, S1 and S2 domains, and nucleocapsid. Samples with positive test results from the 2021 survey underwent repeat testing with enzyme-linked immunosorbent assay to detect anti-nucleocapsid IgG antibodies. Prevalence rates according to gender and age groups, together with their respective 95% confidence intervals (CIs), were calculated. RESULTS: Overall, the proportion of samples with positive test results was 2/353 in 2019 and 22/363 in 2021, with an estimated seroprevalence of 0.27% (95% CI 0-1.86) and 6.21% (95% CI 3.9-9.31) in 2019 and 2021 respectively. CONCLUSION: Results of this study support the hypothesis that the virus was circulating in Italy as early as autumn 2019. The role of these early cases in broader transmission dynamics remains to be determined.

Seroprevalence of infection-induced SARS-CoV-2 antibodies among healthcare users of Northern Italy – results from two serosurveys (October-November 2019 – September-October 2021)

Objective To estimate the seroprevalence of SARS-CoV-2 in autumn 2019 (before case zero was identified in Italy) and 2021 among residual sera samples of healthcare users of Piedmont, Northwestern Italy. Methods Two serosurveys were conducted. Samples were tested for the detection of IgG antibodies against the S1 domain of the spike protein, using a semi-quantitative method. Positive samples from the 2019 survey were independently re-tested using a multiplex panel for the detection of IgG antibodies against the receptor-binding domain, S1 and S2, and nucleocapsid (N). Positive samples from the 2021 survey underwent repeat testing with ELISA for the detection of IgG anti-N antibodies. Prevalence rates according to gender and age groups, together with their respective 95% CIs, were calculated. Results Overall, the proportion of positive samples was 2/353 in 2019 and 22/363 in 2021, with an estimated seroprevalence of 0.27% (95% CI 0 – 1.86) and 6.21% (95% CI 3.9 – 9.31), in 2019 and 2021 respectively. Conclusion Results of this study support the hypothesis that the virus was circulating in Italy as early as autumn 2019. The role of these early cases in broader transmission dynamics remains to be determined.