When we last reviewed Arizona's coronavirus pandemic experience in mid-December 2021, we reported the Delta-variant wave looked to be peaking. In fact, we followed up with an update to that article on 21 December 2021 to confirm it.

Since we reported that data, the Omicron-variant of the SARS-CoV-2 coronavirus arrived, with a rate of spread that exceeds each of the previous waves Arizona has experienced. At least, that's what immediately leaps out in the newest update to our chart tracking Arizona's Coronavirus Pandemic Experience, so let's go straight to it.

The data for cases, hospitalizations, and deaths presented in this chart has been aligned with respect to the approximate date for when those who tested positive, were admitted to hospital, or died would have first been exposed to SARS-CoV-2 coronavirus variants. Presenting the data this way makes it possible to visually identify when the incidence of infection changes. Having that information often makes it possible to identify significant events that affected the trends for COVID infections.

Based on Arizona's data for cases and for new hospital admissions, the Omicron variant of the coronavirus began noticeably spreading approximately on or around 19 December 2021. That's the weekend before the Christmas holiday, which points to public events like shopping, Phoenix' Fiesta Bowl Parade, and pre-holiday social events as the likely venues in which infections of the Omicron coronavirus variant took hold in the state. Unlike the most recent uptrend, few high-attendance sporting events took place Arizona during that period. We likewise expect to see similar liftoff in the data for COVID deaths as that much longer lagging data becomes available.

Behind the scenes, we've looked at new hospital admission data that has not yet been added to this chart because it is less than 95% of the value where it will stabilize for the indicated dates. Based on that partially complete information, we anticipate the data for COVID hospitalizations will parallel the rapid increase already evident for cases confirmed by testing.

Meanwhile, the data for COVID deaths in Arizona during this period is far too incomplete as yet to add an additional confirmation of the 19 December 2021 date marking the arrival of widespread Omicron-variant coronavirus infection in Arizona. The state's data for ICU admissions however points to 19 December 2021 as the kickoff date for the spread of Omicron-variant COVID cases, assuming a 13-day lag from initial exposure, which we see with COVID-infected ICU patients beginning to increase after 1 January 2022. That change in trend may be seen in Arizona's ICU bed usage chart.

While rising in response to Omicron-variant cases, ICU bed usage data points to a lower growth rate for serious cases requiring ICU facilities at this time.

Arizona's ICU COVID-19 bed usage chart also points to an unusual development, in which the number of Arizona's intensive care units was arbitrarily reduced by about 90 units on 18 December 2021, with the impact concentrated in beds being used by non-COVID ICU patients. We have found no contemporary reporting to explain why that happened. Since we previously reported Arizona's available supply of ICU beds was becoming pinched in early December 2021, we believe that decision should be called into question given the developing situation with the Omicron variant in the state.

We'll close with some better news. Going back to the first chart, we see the rate at which new COVID cases are occurring in Arizona has begun to slow in the period since 1 January 2022. Though it is still rising, which we anticipate will continue for several weeks, each previous wave of COVID infections in Arizona was preceded by a similar deceleration before peaking.

Previously on Political Calculations

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

• Omicron Arrives in Arizona
• Upswing in Arizona COVID Cases Shows Signs of Peaking, Crowded ICUs
• COVID-19 Cases on Upswing in Arizona
• Arizona's COVID Hospital Admissions Unexpectedly Plunge
• All Indicators Confirm COVID Third Wave Receding in Arizona
• Arizona's Third COVID Wave Peaks and Begins to Recede
• Arizona COVID Cases Rising in Third Wave
• Arizona COVID Cases on Slow Uptrend in Summer 2021
• Increase in Arizona COVID Cases from Border Migration Crisis Stabilizing
• COVID-19 and the 2021 Border Migration Crisis in Arizona
• Improving COVID Trends Bottom and Flatline in Arizona
• Surge of Migrants, Lifting of Business Capacity Limits Change Arizona COVID Trends
• COVID-19 in Retreat in Arizona With Vaccines Gaining Traction
• The Ebb and Flow of COVID-19 in Arizona's ICUs
• Arizona's Plunging COVID-19 Caseloads and the Vaccines
• Arizona Enters Downward Trend for COVID-19 After Second Peak
• Arizona Passes Second COVID-19 Peak
• A Tale of Two States and the Coronavirus
• COVID-19 Questions, Answers, and Lessons Learned from Arizona
• The Deadly Intersection of Anti-Police Protests and COVID-19
• 2020 Campaign Events Drive Surge in Arizona COVID Cases
• Arizona Arrives at Critical Junction for Coronavirus Cases
• Arizona To Soon Reach A Critical Junction For COVID-19
• Getting More Than Care from Arizona's COVID ICU Beds
• Arizona's Decentralized Approach to Beating COVID
• Going Back to School with COVID-19
• Arizona Turns Second Corner Toward Crushing Coronavirus
• Arizona's Coronavirus Crest in Rear View Mirror
• The Coronavirus Turns a Corner in Arizona
• A Delayed First Wave Crests in the U.S. and a Second COVID-19 Wave Arrives
• The Coronavirus in Arizona
• A Closer Look at COVID-19 Deaths in Arizona
• The New Epicenter of COVID-19 in the U.S.
• How Long Does a Serious COVID Infection Typically Last?
• How Deadly is the COVID-19 Coronavirus?
• Governor Cuomo and the Coronavirus Models
• How Do False Test Outcomes Affect Estimates of the True Incidence of Coronavirus Infections?
• How Fast Could China's Coronavirus Spread?

References

Political Calculations has been following Arizona's experience with the coronavirus experience from almost the beginning, because the state makes its high quality data publicly available. Specifically, the state's Departent of Health Services reports the number of cases by date of test sample collection, the number of hospitalizations by date of hospital admission, and the number of deaths by date recorded on death certificates.

This data, combined with what we know of the typical time it takes to progress to each of these milestones, makes it possible to track the state's daily rate of incidence of initial exposure to the variants of the SARS-CoV-2 coronavirus using back calculation methods. Links to that data and information about how the back calculation method works are presented below:

Arizona Department of Health Services. COVID-19 Data Dashboard: Vaccine Administration. [Online Database]. Accessed 17 January 2022.

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.