López, Mariana GChiner-Oms, ÁlvaroGarcía de Viedma, DaríoRuiz-Rodriguez, PaulaBracho, Maria AlmaCancino-Muñoz, IrvingD'Auria, Giuseppede Marco, GriseldaGarcía-González, NerisGoig, Galo AdrianGómez-Navarro, InmaculadaJiménez-Serrano, SantiagoMartinez-Priego, LlúciaRuiz-Hueso, PaulaRuiz-Roldán, LidiaTorres-Puente, ManuelaAlberola, JuanAlbert, EliseoAranzamendi Zaldumbide, MaitaneBea-Escudero, María PilarBoga, Jose AntonioBordoy, Antoni ECanut-Blasco, AndrésCarvajal, AnaCilla Eguiluz, GustavoCordón Rodríguez, Maria LuzCosta-Alcalde, José Jde Toro, Maríade Toro Peinado, InmaculadaDel Pozo, Jose LuisDuchêne, SebastiánFernández-Pinero, JovitaFuster Escrivá, BegoñaGimeno Cardona, ConcepciónGonzález Galán, VerónicaGonzalo Jiménez, NievesHernáez Crespo, SilviaHerranz, MartaLepe, José AntonioLópez-Causapé, CarlaLópez-Hontangas, José LuisMartín, VicenteMartró, ElisaMilagro Beamonte, AnaMontes Ros, MilagrosaMoreno-Muñoz, RosarioNavarro, DavidNavarro-Marí, José MaríaNot, AnnaOliver, AntonioPalop-Borrás, BegoñaParra Grande, MónicaPedrosa-Corral, IrenePérez González, Maria CarmenPérez-Lago, LauraPérez-Ruiz, MercedesPiñeiro Vázquez, LuisRabella, NuriaRezusta, AntonioRobles Fonseca, LorenaRodríguez-Villodres, ÁngelSanbonmatsu-Gámez, SaraSicilia, JonSoriano, AlexTirado Balaguer, María DoloresTorres, IgnacioTristancho, AlexanderMarimón, José MaríaSeqCOVID-Spain consortiumCoscolla, MireiaGonzález-Candelas, FernandoComas, Iñaki2025-01-072025-01-072021-09-30https://hdl.handle.net/10668/26458The coronavirus disease 2019 (COVID-19) pandemic has affected the world radically since 2020. Spain was one of the European countries with the highest incidence during the first wave. As a part of a consortium to monitor and study the evolution of the epidemic, we sequenced 2,170 samples, diagnosed mostly before lockdown measures. Here, we identified at least 500 introductions from multiple international sources and documented the early rise of two dominant Spanish epidemic clades (SECs), probably amplified by superspreading events. Both SECs were related closely to the initial Asian variants of SARS-CoV-2 and spread widely across Spain. We inferred a substantial reduction in the effective reproductive number of both SECs due to public-health interventions (Re enCOVID-19Communicable Disease ControlHumansIncidenceModels, StatisticalPhylogenyPhysical DistancingQuarantineSARS-CoV-2Severity of Illness IndexSpainresearch article34594042open access10.1038/s41588-021-00936-61546-1718PMC8481935https://www.nature.com/articles/s41588-021-00936-6.pdfhttps://pmc.ncbi.nlm.nih.gov/articles/PMC8481935/pdf