Across the globe, COVID-19 has infected more than 18 million people to date and has killed hundreds of thousands — and the United States has been hit especially hard.
Although the U.S. comprises just 4.2% of the global population, it accounted for approximately 33% of all reported infections by the end of April.
In a new study, researchers showed the majority of U.S. states eventually imposed stay-at-home orders, and those orders appear to have significantly slowed the spread of the disease for the nation as a whole.
They also showed a state-by-state breakdown of how quickly COVID-19 spread before and after lockdown orders.
The research was conducted by a team at Brown University.
The team calculated the pandemic doubling time — the amount of time it takes for the number of cases to double — on both a national level and for individual states. An increase in doubling time indicates a slowing pandemic.
This map highlights the percentage increase in epidemic doubling time between pre-stay-at-home order and during stay-at-home order time periods, by state.
Before the effects of widespread lockdowns became apparent — from March 4 until April 4 — the national pandemic doubling time was 2.68 days.
This doubling time increased significantly, to an average of 15 days, in the period between April 5 and April 30.
In other words, the number of cases doubled in less than three days before mitigation measures were put into place. In contrast, after mitigation measures, the number of cases took more than two weeks to double.
But while doubling time increased in all states, the rate of increase varied.
On average, the 45 states with stay-at-home orders in place added about 12.27 days to their doubling time, indicating a significant slowing of disease spread.
Meanwhile, the five states without stay-at-home orders — Arkansas, Iowa, Nebraska, North Dakota, and South Dakota — added only about six days to their doubling time, and four of these states exhibited some of the worst doubling rates in the nation.
The team says understanding the trajectory of the epidemic in the U.S. is critical, and measuring the impact of stay-at-home orders on epidemic growth offers evidence for current and future COVID-19 control and containment measures.
They hope that these findings contribute to a growing body of evidence aimed at studying the full course of COVID-19 in America.
One author of the study is Mark Lurie, an associate professor of epidemiology.
The study is published in the Journal of Infectious Diseases.
Copyright © 2020 Knowridge Science Report. All rights reserved.
