In the United States, flu activity (measured by the percentage of respiratory samples submitted for flu tests that gave positive results) began to increase in early November 2019 and >20% of samples were positive during 15 December 2019-7 March 2020, after which activity decreased sharply. In the week of 22 March 2020, when the number of samples tested remained very high, the percentage positivity dropped to 2.3%, and since the week of 5 April 2020, it has remained <1%. The median number of flu-tested specimens each week decreased from 49,696 during 29 September 2019-9 February 2020, to 19,537 during 1 March 2020-16 May 2020, a decrease of 61%. During these same two periods, flu activity decreased by 98%\cite{Lasry_2020}