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 MaríaCoscolla, MireiaGonzález-Candelas, FernandoComas, Iñaki2022-11-142022-11-142021Nat Genet . 2021 Oct;53(10):1405-1414. doi: 10.1038/s41588-021-00936-6. Epub 2021 Sep 30.http://hdl.handle.net/20.500.12105/15129The 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 < 1), also reflected in the replacement of SECs by a new variant over the summer of 2020. In summary, we reveal a notable difference in the initial genetic makeup of SARS-CoV-2 in Spain compared with other European countries and show evidence to support the effectiveness of lockdown measures in controlling virus spread, even for the most successful genetic variants.engVoRhttp://creativecommons.org/licenses/by/4.0/Models, StatisticalCOVID-19Communicable Disease ControlHumansIncidencePhylogenyPhysical DistancingQuarantineSARS-CoV-2Severity of Illness IndexSpainAtribución 4.0 Internacional3459404253101405-141410.1038/s41588-021-00936-61546-1718Nature geneticsopen access