Four weeks ago, we covered the arrival of the Omicron-wave of the coronavirus pandemic in Arizona. Four weeks later, the weak variant is well on its way to fading into the obsurity of history.

Despite being impressively contagious and easy to spread, the Omicron variant of the SARS-CoV-2 coronavirus lacked the severity that characterized previous waves of coronavirus infections in Arizona. We confirm that's the case with the state's high quality data on COVID-related hospitalization and deaths, where we find neither have trended in the state in th elevated way that cases have. We've visualized these data series, where we've aligned the data for each according to when Arizonans who became infected with COVID-19 were most likely first exposed to the viral infection.

Based on Arizona's data for cases, new hospital admissions, and deaths, the Omicron variant of the coronavirus began noticeably spreading approximately in the period from 15 through 19 December 2021. That covers 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.

After lifting off, the surge in COVID infections went on to peak in the period from 31 December 2021 through 7 January 2022, pointing to the end of the holiday season and its related social gatherings as a leading contributor to what is developing into a rapid decline in the incidence of new infections.

The data for deaths is remarkable because Arizona's wave of delta-variant coronavirus infections has largely blended with the omicron-variant in such a way that the overall trend in deaths has fallen within a relatively narrow range since early November 2021. Or rather, as deaths attributed to the more deadly delta-variant waned, they were replaced almost one-for-one by the much less deadly omicron-variant, where infections were occurring in much higher numbers. We anticipate that pattern will hold until the lagging data for deaths catches up to the rapidly declining trends for both cases and hospitalizations in the state.

Arizona's data for ICU bed usage confirms the rapid decline in omicron-related COVID-19 cases in recent weeks.

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. The data confirms Arizona's hospitals have maintained high rates of ICU bed utilization, with hospital operators working to keep as many beds occupied with both COVID and non-COVID patients as they could. We have not yet however found any explanation for the reduction in ICU beds in Arizona in mid-December 2021.

We're coming up on the two year anniversary of the coronavirus pandemic in Arizona, which if the positive trends now developing continue to hold, will mark our last regular entry for this series as the pandemic appears to be approaching its end.

Previously on Political Calculations

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

• Omicron Rapidly Fades in Arizona
• 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 February 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.