R0 or reproduction number is shown on the Y axis. R0 below 1 indicates the virus is expiring for this wave of infection.
Igor Mandel, Ph.D.:
Estimation of the reproductive numbers in time, USA and East Coast (data presented from the day when the states had more than 20 cases; data source, John Hopkins University; three states include New York, New Jersey, and Connecticut; six states — these three plus Massachusetts, Pennsylvania, and Delaware).