The new website rt.live calculates the rate at which COVID-19 is spreading in all 50 states, measured by the average number of people who become sick from an infectious person, Vox reports.
Created by Instagram co-founders Kevin Systrom and Mike Krieger, the site tracks the effective reproduction rate (Rt) of COVID-19 infections. Charts on the site can reveal how the virus's spread over the past three weeks has been affected by intervention strategies, like stay-at-home measures.
A Rt value of one means each case causes, on average, one new case. If the value is less than one, the spread of the disease is slowing. The higher the Rt number is, the worse the spread.
As of April 22, Arkansas had an Rt of 2.26, the highest effective reproduction rate, while South Carolina had the lowest Rt at 0.06. Four of the five states without shelter-in-place orders — Nebraska, North Dakota, Iowa and Arkansas — had rates above one.
Tracking the effective reproductive rate is a reasonable way to look at how well intervention strategies are working, Natalie Dean, PhD, assistant professor of biostatistics at Gainesville-based University of Florida, told Vox. However, Dr. Dean said a low Rt by itself isn't reason enough to end shelter-in-place measures.