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00925njm 22002777a 4500 dc Perez-Olmeda, Mayte author Saugar, Jose Maria author Fernandez-Garcia, Aurora author Perez-Gomez, Beatriz author Pollan-Santamaria, Marina author Avellón, Ana author Pastor-Barriuso, Roberto author Fernandez de Larrea-Baz, Nerea author Martín, Mariano author Cruz, Israel author Sanmartín, Jose L author Fedele, Cesare Giovanni author Paniagua-Caparros, Jose Leon author Muñoz-Montalvo, Juan F author Blanco, Faustino author Yotti-Alvarez, Raquel author Oteo-Iglesias, Jesus author ENE-COVID Study Group author 2022-04 Background: The main aims of this study were to analyze trends of SARS-CoV-2 anti-nucleocapsid IgG throughout the four rounds of the seroepidemiologic study ENE-COVID, and compare the fourth-round results of two immunoassays detecting anti-nucleocapsid and anti-RBD IgG. Methods: ENE-COVID was developed in 2020 (two phases). Phase one included three rounds carried out in April 27-May 11, May 18-June 1, and June 8-June 22. Phase two included a fourth round in the same cohort (November 16-29). A chemiluminescent microparticle immunoassay was offered to participants in the first three rounds (Abbott; anti-nucleocapsid IgG). In the fourth round, we offered this test and a chemiluminescence immunoassay (Beckman; anti-RBD IgG) to i) a randomly selected sub-cohort, ii) participants who were IgG-positive in any of the three first rounds; and iii) participants who were IgG-positive in the fourth round by point-of-care immunochromatography. Results: 10,153 individuals (82.2% of people invited) participated in the fourth round. Of them, 2595 (35.1% of participants with results in the four rounds) were positive for anti-nucleocapsid IgG in at least one round. Anti-nucleocapsid IgG became undetectable in 43.3% of participants with positive first-round results. In fourth round, anti-nucleocapsid and anti-RBD IgG were detected in 5.5% (321/5827) and 5.4% (315/5827) participants of the randomly selected sub-cohort, and in 26.6% (867/3261) and 25.9% (846/3261) participants with at least one previous positive result, respectively. Conclusions: The IgG response is heterogeneous and conditioned by infection severity. A proportion of SARS-CoV-2 infected population may have negative serologic results in the post-infection months. Pérez-Olmeda M, Saugar JM, Fernández-García A, Pérez-Gómez B, Pollán M, Avellón A, Pastor-Barriuso R, Fernández-de Larrea N, Martín M, Cruz I, Sanmartín JL, Fedele G, Paniagua JL, Muñoz-Montalvo JF, Blanco F, Yotti R, Oteo-Iglesias J; ENE-COVID Study Group. Evolution of antibodies against SARS-CoV-2 over seven months: Experience of the nationwide seroprevalence ENE-COVID study in Spain. J Clin Virol. 2022 Apr;149:105130. 10.1016/j.jcv.2022.105130 1873-5967 1386-6532 Journal of clinical virology: the official publication of the Pan American Society for Clinical Virology 35305377 https://hdl.handle.net/20.500.12105/26184 Antibodies COVID-19 ENE-COVID SARS-CoV-2 Seroprevalence Evolution of antibodies against SARS-CoV-2 over seven months: Experience of the nationwide seroprevalence ENE-COVID study in Spain