Callejas Caballero, IgnacioRuedas López, AlbaBerzosa Sánchez, ArantxaIllán Ramos, MartaJoyanes Abancens, BelénBodas Pinedo, AndrésGuillén Martín, SaraSoto Sánchez, BeatrizGarcía Bermejo, IsabelMolina Arana, DavidAlós, Juan-IgnacioBaos Muñoz, ElviraDelgado Iribarren, AlbertoFuentes Ferrer, Manuel E.Ramos Amador, José Tomás2023-06-222023-06-222022-05-052227-906710.3390/children9050665https://hdl.handle.net/20.500.14352/71623Background: SARS-CoV-2 was a global pandemic. Children develop a mild disease and may have a different rate of seroconversion compared to adults. The objective was to determine the number of seronegative patients in a pediatric cohort. We also reviewed the clinical–epidemiological features associated with seroconversion. Methods: A multicenter prospective observational study during September–November 2020, of COVID-19, confirmed by reverse transcription-polymerase chain reaction. Data were obtained 4–8 weeks after diagnosis. Blood samples were collected to investigate the humoral response, using three different serological methods. Results: A total of 111 patients were included (98 symptomatic), 8 were admitted to hospital, none required an Intensive Care Unit visit. Median age: 88 months (IQR: 24–149). Median time between diagnosis and serological test: 37 days (IQR: 34–44). A total of 19 patients were non-seroconverters when using three serological techniques (17.1%; 95% CI: 10.6–25.4); most were aged 2–10 years (35%, p < 0.05). Univariate analysis yielded a lower rate of seroconversion when COVID-19 confirmation was not present amongst household contacts (51.7%; p < 0.05). Conclusions: There was a high proportion of non-seroconverters. This is more commonly encountered in childhood than in adults. Most seronegative patients were in the group aged 2–10 years, and when COVID-19 was not documented in household contacts. Most developed a mild disease. Frequently, children were not the index case within the family.engAtribución 3.0 Españahttps://creativecommons.org/licenses/by/3.0/es/journal articlehttps://doi.org/10.3390/children9050665https://www.mdpi.com/2227-9067/9/5/665/htmopen accessRT-PCR (reverse transcriptase polymerase chain reaction)SARS-CoV-2COVID-19seroconversionchildrenInmunologíaPediatría2412 Inmunología3201.10 Pediatría