Alliance for Pandemic Preparedness

April 6, 2020

Cryptic transmission of SARS-CoV-2 in Washington State



  • Bedford et al sequenced 346 SARS-CoV-2 genome from samples collected between February 20 and March 15 in Washington State. The majority of infections appeared to have derived from a single introduction event in late January or early February, suggesting cryptic spread of COVID-19 during the months of January and February. 
  • These findings highlight the critical need for widespread surveillance of SARS-CoV-2 community transmission throughout the U.S. and world, even after the current pandemic is brought under control. 

Bedford et al. (Apr 6, 2020). Cryptic transmission of SARS-CoV-2 in Washington State. Pre-print downloaded Apr 6 from