Dr. Gerald just released his latest epidemiology and hospital capacity report. Below is a summary but as always we encourage you to explore the full report for details.

  • Covid-19 cases and hospitalizations are little changed over the past two weeks. We can expect similar levels of viral transmission for the next 4 – 6 weeks before rates begin to substantially improve.

  • Overall, cases are being diagnosed at a rate of 68 per 100K residents per week- in-between the moderate and substantial spread categories.  Case rates will likely remain “stuck” at around the 50 cases per 100K residents per week for the next 4 – 6 weeks owing to more transmissible variants (e.g., B.1.1.7) and continued normalization of behaviors.

  • Test positivity for traditional nasopharyngeal PCR testing is holding steady at 10%.

  • Hospital Covid-19 occupancy is slowly increasing in the ward and ICU. Access to care remains somewhat restricted as overall occupancy remains unseasonably high (85%) while the backlog of medically necessary non-Covid procedures is being addressed.

  • Arizona continues to slip relative to other states when it comes to the percentage of our population that is vaccinated. Arizona now ranks 40th in vaccines administered per capita.

Note: This is the next-to-last regularly scheduled update. Barring unforeseen circumstances, the last report will be published on May 21, 2021. If you have found this report valuable and would like to send a note of appreciation, please e-mail my Department Chair, Dr. Kelly Reynolds at reynolds@arizona.edu


The ASU COVID-19 Modeling Group recently updated their model (April 29, 2021) to incorporate vaccination efficacy and increasing prevalence of the B117 variant. This model is based on their prior work charting the course of the COVID-19 outbreak using a traditional SEIR epidemiological model.

To incorporate the impact of vaccines, the model accounts for a differential effectiveness attributable to the first and second dose, 50% and 95% respectively. Vaccination data are derived from the ADHS dashboard at the state-level and does not account for differential rates or outcomes by age.

The model assumes a single homogenous risk pool throughout the state. Furthermore, their model assumes a B117 variant dominance by the end of May with its associated 60% increase in transmission. No changes due to increased behavioral interactions are modeled.

Figure 3A in the report shows their best-case scenario (gold line) where COVID-19 vaccinations continue at a pace of 50,000 vaccinations per day. Under this scenario, case rates will peak and then begin to decline towards the end of May. Clearly, there is little-to-no risk of a no summer resurgence.

Under their worst-case scenario (blue line) where no new vaccinations are initiated after April 28th , case rates will slowly trend upwards and remain in the substantial category (50 – 100 cases per 100K residents per week) through much of the summer.

However, even under this pessimistic scenario, there is little-to-no risk of a summer resurgence on par with June 2020. Altogether, this is really good news.

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