No new COVID case surge – yet

There has been much talk about a new surge in COVID-19 cases, dubbed the Fourth Surge by CDC director Dr. Rochelle Walensky on 29 March 2021. So I checked it out.

I’ve been watching the dynamics of new COVID-19 cases in the U.S. for several months, posting daily updates to national and state plots on my website. Here’s a plot of the number of new cases per 100,000 population versus the daily change in the number of new cases per 100,000 population as of 25 March 2021 (posted on 26 March 2021).

The data come from The New York Times, based on reports from state and local health agencies[1]. The arrows show the daily changes color-coded by month, starting with January 2021, on the right, and ending with March 2021, on the left. Arrows in the top half point up and right to show increases in the number of new cases, while arrows in the bottom half point down and left to show decreases in the number of new cases. When the number of new cases is changing every day but averaging about the same over time, the arrows form a kind of circle (I call it an orbit). Note the orbit at the far right in mid January 2021, centered at about 70 new cases per 100,000 population.

Let me point out that these data are averaged over 18 days, while the CDC tends to use a seven-day average. The seven-day average tends to be too jittery to track daily changes for this purpose. The jitters in the seven-day average are a result of the various ways that individual states report COVID-19 data, combined with a weird thing that happens with these kinds of data: events tend to be recorded on certain days of the week even if they happened a day or two before.

This plot shows an overall trend of rapidly decreasing numbers of new cases since 16 January 2021, when it peaked at over 71 new cases per 100,000 population, down to around 20 cases per 100,000 population in March 2021. In March this trend ended, however, stalling first at about 20 new cases per 100,000 population, then slowly decreasing to slightly less than 18 new cases per 100,000 population on 23 March 2021.

Then with two days of increases – 24 and 25 March – the trend implied a worsening – a possible new surge? Fast forward to 31 March 2021, shown in the next plot.

Note that the uptick on 25 March was followed by a down tick on 26 March, and the subsequent five days saw a tight orbit about approximately 19 new cases per 100,000 population. Dodged that bullet!

On the national level, anyway, but some states are seeing rapid increases in the new cases that may be a sign of worse times to come. See my website for details.

[1]The New York Times. (2020). Coronavirus (Covid-19) Data in the United States. https://github.com/nytimes/covid-19-data

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