Unexpectedly Intriguing!
19 August 2021

When we last checked in on Arizona's experience during the coronavirus pandemic, back on 15 July 2021, the number of cases in the state had begun to rise in a slow uptrend. Flashing forward in time to a month later, we find that Arizona is now experiencing much more rapid rise, having entered a third wave of coronavirus infections.

In the following chart, we've aligned the rolling seven-day averages for the number of COVID cases, new hospital admissions, and deaths to the approximate date of exposure for the Arizonans affected by the spread of the various strains of the SARS-CoV-2 coronavirus. The chart is presented in linear scale, where you can see the third wave of infections begin to accelerate at the end of June 2021, which coincides with the Phoenix Suns advancing to the finals in the NBA playoffs.

Arizona's Experience During the Coronavirus Pandemic, 15 March 2020 - 4 August 2021

The chart only visualizes where the available data for each date is at least 95% complete, where it takes slightly longer to reach that level of completeness for hospitalizations and longer still for deaths attributed to COVID-19 to be recorded. Since these data series are difficult to see in this first chart, here is the same data presented with the vertical scale shown in logarithmic scale.

Arizona's Experience During the Coronavirus Pandemic, 15 March 2020 - 4 August 2021, Logarithmic Scale

This chart has quickly become our favorite way to visualize this data, because with the data for each series indexed to the approximate date of initial exposure to coronavirus infection, we can easily see the data for each series has generally paralleled each other in the previous waves.

That characteristic is significant here because we can directly see the impact the COVID vaccines have had in reducing the rate of hospitalizations, which are rising much more slowly than would be predicted by the rate of cases. You can see that difference by comparing the dashed blue line which parallels the current trend for cases with the solid green line indicating COVID hospitalizations.

The data series for deaths is still too incomplete for Arizona's third COVID wave to confirm that pattern exists with this data as well, but it would be reasonable to predict it will show a similar pattern as hospitalizations.

Arizona ICU Bed Usage

Arizona's data for ICU bed usage for COVID indicates Arizona's hospitals have begun adapting to the rising number of serious COVID hospitalizations. Hospitals in the state began actively managing their ICUs to make more beds available for COVID patients beginning after the 4 July 2021 holiday, with a notable adjustment in the number of beds set aside for non-COVID patients roughly two weeks later. One month later, the Arizona hospitals added new ICU capacity. These changes are visible in the following chart:

Arizona COVID-19 ICU Bed Usage, 10 April 2020 - 15 August 2021, Logarithmic Scale

Compared to the earlier COVID waves, Arizona hospitals are seeking to accommodate higher numbers of non-COVID patients in ICUs. While that may change, that is an initial indication they see less risk of overwhelming ICUs with COVID patients during Arizona's third wave of coronavirus infections.

Previously on Political Calculations

Here is our previous coverage of Arizona's experience with the coronavirus pandemic, presented in reverse chronological order.


We've continued following Arizona's experience during the coronavirus pandemic because the state's Department of Health Services makes detailed, high quality time series data available, which makes it easy to apply the back calculation method to identify the timing and events that caused changes in the state's COVID-19 trends. This section links that that resource and many of the others we've found useful throughout the coronavirus pandemic.

Arizona Department of Health Services. COVID-19 Data Dashboard: Vaccine Administration. [Online Database]. Accessed 17 August 2021.

Stephen A. Lauer, Kyra H. Grantz, Qifang Bi, Forrest K. Jones, Qulu Zheng, Hannah R. Meredith, Andrew S. Azman, Nicholas G. Reich, Justin Lessler. The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application. Annals of Internal Medicine, 5 May 2020. https://doi.org/10.7326/M20-0504.

U.S. Centers for Disease Control and Prevention. COVID-19 Pandemic Planning Scenarios. [PDF Document]. 10 September 2020.

More or Less: Behind the Stats. Ethnic minority deaths, climate change and lockdown. Interview with Kit Yates discussing back calculation. BBC Radio 4. [Podcast: 8:18 to 14:07]. 29 April 2020.

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