Antibody Response After First and Second BNT162b2 Vaccination to Predict the Need for Subsequent Injections in Nursing Home Residents

Objectives: A massive immunization program was initiated in France in older adults. The aim of the study was to assess the antibody response following BNT162b2 vaccination in nursing home (NH) residents. Methods: Three hundred and sixty-nine NH residents who received two vaccine doses were tested for antibody vaccine response three weeks after the first dose and six weeks after the second dose. We assessed IgG level against SARS-CoV-2 Receptor-Binding Domain (RBD-IgG) and nucleoprotein-IgG (SARS-CoV-2 IgG II Quant and SARS-CoV-2 IgG Alinity assays, Abbott Diagnostics). Results: In NH residents with prior SARS-CoV-2 infection, high RBD-IgG levels (≥ 4,160 AU/mL) were observed after the first dose in 99/129 (76.9%), with no additional antibody gain after the second dose in 74 (74.7%). However, a low RDB-IgG level (<1,050 AU/mL) was observed in 28 (21.7%) residents. The persistence of nucleoprotein-IgG and a longer interval between SARS-CoV-2 infection and the first dose were associated with a higher RDB-IgG response (p<0.0001 and p=0.0013, respectively). In NH residents without prior SARS-CoV-2 infection, RBD-IgG below 50 AU/mL after the first dose predicted failure to reach a significant antibody concentration (≥ 1,050 AU/mL) after the second dose (predictive positive value: 53.5%, sensitivity: 77.6%, specificity: 73.3%). Conclusions: The BNT162b2 vaccine elicits a strong humoral response after the first dose in NH residents with prior SARS-CoV-2 infection, however, about one quarter may need a second injection. NH residents without prior SARS-CoV-2 infection had a low RBD-IgG response after the first dose and over 30% may need a third injection. Funding Information: This work was funded by the Montpellier University Hospital, Muse I-SITE Program Grant, University of Montpellier. Declaration of Interests: The authors declare that there are no conflict of interests or personal relationships that could have appeared to influence the work reported in this paper. Ethics Approval Statement: Subjects provided an informed consent and the study was approved by the Montpellier University Hospital institutional review board (IRB-MTP_2020_06_202000534 and IRB-MTP _2021_04_202000534).