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Well over a year into the Covid-19 pandemic, visualizations of case data have become ubiquitous. By far, the most popular metric that public health officials and media outlets rely on is the daily count of new cases.

But as the Delta wave picked up steam in the U.S., STAT introduced a new metric that helps detect early changes in case trends: case acceleration.


On this page, STAT is making available for the first time real-time acceleration data for U.S. states and territories.

Charts on this page use data from the Centers for Disease Control and Prevention, the Center for Systems Science and Engineering at Johns Hopkins University, and Our World in Data to calculate the rate of weekly case acceleration, based on daily case counts. Charts on this page will be updated daily as new data become available.

What is acceleration?

A car’s speedometer tells you how fast that car is moving at any given time. The scientific term for this is velocity. Acceleration is a measure of the change in velocity, in other words how fast something is speeding up or slowing down.


The daily count of new Covid-19 cases can be thought of as the pandemic’s velocity. If velocity tells us how bad the pandemic is at any given time, acceleration tells us how fast things are getting better or worse.

In these charts, when the values are positive, new case counts are increasing, and when the values are negative, new case counts are falling. Highlighted in red, we can see more clearly each wave’s intensity and duration.

What has changed

Since STAT’s analysis of acceleration data in June, the course of the Delta wave has progressed significantly.

Missouri, the first state to experience prolonged positive acceleration this summer, now appears past its peak with cases consistently slowing down.

Likewise, many of the southern states where the Delta wave has been felt most acutely — Florida, Alabama, Arkansas, and Louisiana — are also now seeing sustained deceleration in cases.

In the case of Louisiana, however, it should be noted that the state is currently recovering from the impacts of Hurricane Ida, which could be affecting the state’s reporting ability, thus skewing the data downward.

However, other states like West Virginia, South Carolina, and Georgia, continue to see sustained case acceleration.

J. Emory Parker/STAT Sources: JHU CSSE, WHO, CDC, Our World in Data

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