Daily New Cases: Explained

Daily new cases, also known as incidence in epidemiology, is the number of new COVID cases per day per unit of population. We use a more clear term, “daily new cases” that doesn’t require expert knowledge and calculate it per 100,000 people in states and counties.

Daily new cases answers the question: “How many new infections are in my area each day?” Because we can’t test our entire population, we don’t know how many total cases are in a given population. Measuring daily new cases gives us a way to gauge new COVID cases without having to test an entire population.

Starting with one infected person, every day 3 more infected are added (thus there are 4 infected on day 2, and 7 on day 3).

In the example to the right, the number of daily new cases is 3. On day one, there is a single case, but each day there are 3 new cases x per 100k people.

You can see that daily new cases, or incidence, is not a measure of the total number of cases.

While the infection rate shows how many people one person will infect while contagious, daily new cases tells us how many newly infected people are spreading at that rate. The two metrics go hand-in-hand. 

Here’s a video that helps explain daily new cases:

How does Covid Act Now rate Daily New Cases?

Covid Act Now takes an average of new COVID cases over the past seven days and divide that by 100,000. This way, we can see how many new cases there are per 100,000 people in a county or state. 

Our risk levels are based on the percent of a population that will be infected if the rate continues for one year. If critical (red) rates continue, more than 50% of a population will be infected. If high (orange) rates continue, between 10-50% of the population will be infected. If medium (yellow) rates continue, 1-10% of the population will be infected. If low (green) rates continue, less than 1% of the population will be infected. 

Let’s look at daily new cases in Nevada on July 12, below. There were 24.2 daily new cases (per 100,000) and the infection rate was 1.13.  The population of Nevada is 3.08 million, so 27.3 people per 100,000 is 841 people.

Daily new cases on July 12th, 2020 are at 24.2 per 100,000 people. We see the graph line shift abruptly upward after this point.

Where does our data come from for this metric?

To calculate daily new cases, we use new positive cases from The New York Times.

Daily New Cases is just one of several important metrics to determine how well your state or county is doing in the fight against COVID. Learn more about test positivity, infection rate, ICU headroom used, and contact tracing. For a description of assumptions and methodology, please see our references and assumptions document, along with our data sources presentation.

Check out our Youtube Channel for our educational videos.

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