WHO updates coronavirus face mask guidance, says face shields are inferior alternative Fox NewsNew study suggests COVID-19 arrived in the U.S. last December without anyone knowing Yahoo LifestyleA new study found coronavirus may have been in the US in December. That doesn't mean you'll ever know if you had it then CNNIt Now Looks Like COVID-19 Was Already in The US in December 2019 ScienceAlertDo SARS-CoV-2 mutations affect its transmissibility?