Perez-Gomez, BeatrizPastor-Barriuso, RobertoFernandez de Larrea-Baz, NereaHernán, Miguel APerez-Olmeda, MayteOteo-Iglesias, JesusFernandez-Navarro, Pablo LFernandez-Garcia, AuroraMartín, MarianoCruz, IsraelSanmartín, José LPaniagua-Caparros, Jose LeonMuñoz-Montalvo, Juan FBlanco, FaustinoYotti-Alvarez, RaquelPollan-Santamaria, Marina2026-01-272026-01-272023-05Beatriz Pérez-Gómez, Roberto Pastor-Barriuso, Nerea Fernández-de-Larrea, Miguel A. Hernán, Mayte Pérez-Olmeda, Jesús Oteo-Iglesias, Pablo Fernández-Navarro, Aurora Fernández-García, Mariano Martín, Israel Cruz, José L. Sanmartín, José León-Paniagua, Juan F. Muñoz-Montalvo, Faustino Blanco, Raquel Yotti, and Marina Pollán: SARS-CoV-2 Infection During the First and Second Pandemic Waves in Spain: the ENE–COVID Study American Journal of Public Health 113, 533_544, https://doi.org/10.2105/AJPH.2023.307233.https://hdl.handle.net/20.500.12105/27185Objectives. To describe participant characteristics associated with severe acute respiratory syndrome coronavirus 2 infection in Spain's first 2 COVID-19 waves per the Spanish National Seroepidemiological Survey of SARS-CoV-2 Infection (ENE-COVID). Methods. A representative cohort of the noninstitutionalized Spanish population, selected through stratified 2-stage sampling, answered a questionnaire and received point-of-care testing April to June 2020 (first wave: n = 68 287); previously seronegative participants repeated the questionnaire and test November 2020 (second wave: n = 44 451). We estimated seropositivity by wave and participant characteristics, accounting for sampling weights, nonresponse, and design effects. Results. We found that 6.0% (95% confidence interval [CI] = 5.7%, 6.4%) of Spain's population was infected by June and 3.8% (95% CI = 3.5%, 4.1%) more by November 2020. Both genders were equally affected. Seroprevalence decreased with age in adults 20 years and older in the second wave; socioeconomic differences increased. Health care workers were affected at 11.1% (95% CI = 9.0%, 13.6%) and 6.1% (95% CI = 4.4%, 8.5%) in the first and second waves, respectively. Living with an infected person increased infection risk to 22.1% (95% CI = 18.9%, 25.6%) in the first and 35.0% (95% CI = 30.8%, 39.4%) in the second wave. Conclusions. ENE-COVID characterized the first 2 pandemic waves, when information from surveillance systems was incomplete. (Am J Public Health. 2023;113(5):533-544. https://doi.org/10.2105/AJPH.2023.307233).engVoR368933701135533-54410.2105/AJPH.2023.307233American Journal of Public Healthmetadata only access