ABSTRACT
BACKGROUND AND AIM: Dialysis patients are a high-risk population and have a reduced immune response to vaccination against SARS-CoV-2. The aim of this study was to assess the humoral response to homologous Gam-COVID-Vac (Sputnik V) and heterologous Sputnik V/mRNA-1273 (Moderna) vaccination in dialysis patients. The vaccination scheme depended on dose availability and the prioritization of risk populations as established by the Argentine Ministry of Health. METHODS: Previous COVID-19 infection was determined in symptomatic patients. Binding IgG antibodies against the spike (S) receptor-binding domain (RBD) of SARS-CoV-2 (anti-S-RBD) concentration was assessed between 3 and 16 weeks after the boost dose. Anti-S-RBD antibodies were quantified using the Abbott Diagnostics SARS-CoV-2 IgG II Quant chemiluminescent microparticle immunoassay (CMIA) on an Architect i2000 SR and an Alinity I analyzer (Abbott Diagnostics, Abbott Park, Illinois, USA). To standardize the results to WHO binding antibody units (BAU), a correction factor for Abbott arbitrary units (AU) was applied where 1 BAU/mL equals 0.142 AU, as previously established by Abbott with the WHO international standard NIBSC 20-136. Following the manufacturer's recommendations, samples were considered reactive for anti-S-RBD when titers were above 50 AU/mL (7.2 BAU/mL). An 80% protective effect (PROT-80) against symptomatic SARS-CoV-2 infection was assumed when anti-S-RBD titers were 506 BAU/ml or higher. Charlson Comorbidity Index (CCI) score was classified as mild = 1-2, moderate = 3-4, and severe ≥ 5. Side effects were evaluated until day 7 by patients´ self-reported questionnaire. RESULTS: One hundred seven participants were enrolled [n = 84 homologous (SpV/SpV), nn 23 heterologous (SpV/Mod)]. Median (IQR) age was 64 (50-75) years old and 79 (73.8%) were male. Additionally, 19 (22.6%) of the SpV/SpV and 4 (17.4%) of the SpV/Mod group had a prior confirmed SARS-CoV-2 infection (p = 0.589). In the overall population, 103 patients reached seroconversion (96.3%). Anti-S-RBD IgG median titers (IQR) were higher in the heterologous [1222 (288-5680) BAU/mL] than in the homologous scheme [447 (100-1551) BAU/mL], p = 0.022. In a linear model adjusted for age, gender, days from first vaccination to boost dose and days from the boost dose to the anti-S-RBD IgG determination, previous SARS-COV-2 infection (B: 2062.2; CI95: 1231.8-2892.6; p < 0.001), and SpV/Mod vaccination scheme (B: 1294.6; CI95: 435.58-2147.6; p = 0.003) were independently associated with anti-S-RBD levels. Finally, a higher frequency of adverse effects was associated with the heterologous scheme, although they were well tolerated by all individuals. CONCLUSIONS: The present study provides evidence that the homologous SpV/SpV and heterologous SpV/Mod schemes showed good efficacy and safety in patients on chronic dialysis. These results could be useful for designing future vaccination strategies, especially aimed at this risk group.