Immunological response against SARS-CoV-2 following full-dose administration of Comirnaty® COVID-19 vaccine in nursing home residents

OBJECTIVES: The current study was aimed at examining SARS-CoV-2 immune responses following two doses of Comirnaty® COVID-19 vaccine among elderly people in nursing homes. METHODS: A prospective cohort study in a representative sample from nursing homes in Valencia (n = 881; males: 271, females 610; median age, 86 years) recruited residents using a random one-stage cluster sampling approach. A lateral flow immunochromatography device (LFIC) (OnSite COVID-19 IgG/IgM Rapid Test; CTK BIOTECH, Poway, CA, USA) was used as the front-line test for detecting SARS-CoV-2-Spike (S)-specific antibodies in whole blood obtained using a fingerstick. Residents returning negative LFIC results underwent venipuncture and testing for presence of SARS-CoV-2-S-reactive antibodies and T cells using the Roche Elecsys® Anti-SARS-CoV-2 S (Roche Diagnostics, Pleasanton, CA, USA), the LIAISON® SARS-CoV-2 TrimericS IgG assay (Diasorin S.p.A, Saluggia, Italy) and by flow cytometry, respectively. RESULTS: The SARS-CoV-2-S antibody detection rate in nursing home residents was 99.6% (283/284) and 98.3% (587/597) for SARS-CoV-2 recovered and naïve residents, respectively, within a median of 99 days (range 17–125 days) after full vaccination. Three out of five residents lacking SARS-CoV-2-S antibodies had detectable S-reactive CD8(+) and/or CD4(+) T cells. In addition, 50/50 and 40/50 participants with detectable SARS-CoV-2 antibodies also had SARS-CoV-2-S-reactive interferon-γ-producing CD4(+) and CD8(+) T cells, respectively. DISCUSSION: The Comirnaty® COVID-19 vaccine is highly immunogenic in nursing home residents.