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Although a limited number of SARS-CoV-2 introductions were reported in January and February 2020 (refs.\n                    <jats:sup>8,9<\/jats:sup>\n                    ), the narrowness of the initial testing criteria, combined with a slow growth in testing capacity and porous travel screening\n                    <jats:sup>10<\/jats:sup>\n                    , left many countries vulnerable to unmitigated, cryptic transmission. Here we use a global metapopulation epidemic model to provide a mechanistic understanding of the early dispersal of infections and the temporal windows of the introduction of SARS-CoV-2\u00a0and onset of local transmission in Europe and the USA. We find that community transmission of SARS-CoV-2 was likely\u00a0to have been present in several areas of Europe and the USA by January 2020, and estimate that by early March, only 1 to 4 in 100 SARS-CoV-2 infections were detected by surveillance systems. The modelling results highlight international travel as the key driver of the introduction of SARS-CoV-2, with possible introductions and transmission events as early as December 2019 to\u00a0January 2020. We find a heterogeneous geographic distribution of cumulative infection attack rates by 4 July 2020, ranging from 0.78% to 15.2% across US states and 0.19% to 13.2% in European countries. Our approach complements phylogenetic analyses and other surveillance approaches and provides insights that can be used to design innovative, model-driven surveillance systems that guide enhanced testing and response strategies.\n                  <\/jats:p>","DOI":"10.1038\/s41586-021-04130-w","type":"journal-article","created":{"date-parts":[[2021,10,25]],"date-time":"2021-10-25T12:02:36Z","timestamp":1635163356000},"page":"127-132","update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":100,"title":["Cryptic transmission of SARS-CoV-2 and the first COVID-19 wave"],"prefix":"10.1038","volume":"600","author":[{"given":"Jessica T.","family":"Davis","sequence":"first","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5955-1929","authenticated-orcid":false,"given":"Matteo","family":"Chinazzi","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5559-3064","authenticated-orcid":false,"given":"Nicola","family":"Perra","sequence":"additional","affiliation":[]},{"given":"Kunpeng","family":"Mu","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2894-0489","authenticated-orcid":false,"given":"Ana","family":"Pastore y Piontti","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1753-4749","authenticated-orcid":false,"given":"Marco","family":"Ajelli","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3884-0921","authenticated-orcid":false,"given":"Natalie E.","family":"Dean","sequence":"additional","affiliation":[]},{"given":"Corrado","family":"Gioannini","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6393-1943","authenticated-orcid":false,"given":"Maria","family":"Litvinova","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5117-0611","authenticated-orcid":false,"given":"Stefano","family":"Merler","sequence":"additional","affiliation":[]},{"given":"Luca","family":"Rossi","sequence":"additional","affiliation":[]},{"given":"Kaiyuan","family":"Sun","sequence":"additional","affiliation":[]},{"given":"Xinyue","family":"Xiong","sequence":"additional","affiliation":[]},{"suffix":"Jr","given":"Ira M.","family":"Longini","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3127-1757","authenticated-orcid":false,"given":"M. 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