Delta Surge Update – Demographics Focus 8/13/21

Hospitalization (Arizona)

One question that hasn’t been well addressed in the media (all political bents) is whether the COVID Delta surge was driving hospitalization and who, indeed, was being hospitalized. My thinking is that this is our prime metric of the danger of a COVID surge these days. Here’s a chart showing the Arizona hospitalization numbers by demographic. It’s a bit messy for a couple of reasons: 1) Arizona keeps “catching up” on hospitalization numbers by dumping large count backlogs into a single day. I suspect this is a hard metric to keep up with due to all the hospital systems in the state and their state of enthusiasm (?) about reporting data… 2) I stopped capturing the daily snapshot from AZDHS’ web site sometime in May when the data got really boring and moved to weekly (or so). This means my trends aren’t as granular as before, but they’re still accurate.

Arizona Hospitalization (beds used) Data by Age – AZDHS data, collected by T.N. – 8/13/21

What do we see above? Note that at the left of the chart, the hospitalization by age is fairly random and driven by low numbers and statistics. However, if you can ignore the glitch in the middle, the trend is pretty clear towards the right (the Delta Surge). Hospitalization numbers are clearly trending up (but are still not significantly higher than in May. What does this trend reveal? Surprisingly, the over65 age group is still getting hospitalized at much higher rates than their percentage of the population would indicate. No way to know if these are vaccinated people or not. That’s a big gap in the data. They’re matched in numbers by the much-larger 20-44 age group and followed closely by the 45-54 and 55-64 groups. The under 20 age group remains the least hospitalized. This seems to go against some of the news reports that are indicating that the Delta variant is having more severe outcomes in the youngest cases. That doesn’t seem to be the case right now in Arizona at least.

Below I’m showing the hospitalization numbers for all age demographics. As you can see, the Delta surge (furthest right) has not been surging in the hospitals the same way the earlier two surges did. Keep your eye on this chart as things move forward.

AZ Hospitalization since 4/20 (

Cases – Pima County

In my county (Pima) the Delta surge has resulted in proportionately less cases than in the much-larger Maricopa County. My suspicion is that this is due to the notably higher vaccination rates in Pima County. But again, the big question is which demographics are getting infected during the current surge?

Pima County Cases by Age Demographic – 8/13/21

Again, ignoring the loss of granularity by my moving to weekly data capture, you can see the trending on cases from the lows of May until now. It’s no surprise that the 20-44 age group is leading the case counts. In general, across Arizona, this group is much less likely than older demographics to get vaccinated. Plus, there’s more of them. However, the most interesting part of this chart is that the under 20 group is the next highest increase in cases. This group is largely unvaccinated, but it’s not clear how many of them are between 12 and 20 and how many are under 12. This is an error in data collection “strategy” that’s been a problem throughout COVID. Perhaps no one expected at the start that the under 16 demographic (school age) would be so interesting for this pandemic. The rest of the demographics (more vaccination and older) are barely seeing any case rate uptick since May. So, again, fairly surprising that the youngest demographics are the primary ones getting the Delta variant of COVID. No doubt “breakthrough” cases are happening in vaccinated people, but perhaps they’re not symptomatic enough to get counted. Or maybe there are just very few of them (despite what the headlines would indicate).

I just show Pima County here, but statewide, the trend is similar. At the state level, the case rates in the older demographics are slightly higher than Pima county and the younger demographic case rates are noticeably higher. This, again, is driven by the much higher rates and lower vaccination in huge Maricopa County.


There isn’t much change to death rates during the Delta surge from the low period of May. Deaths are still very low, as you can see from the height of the stacked blue and red bars in the chart below. The only thing that *might* be interesting is that the ratio of deaths in the over65 demographic to deaths in every other demographic is much lower now. Sometimes we see this when deaths are low, but during the two previous surges, this ratio trended between 2.5 and 4. Right now it ranges around 2 or lower. This ratio is the green line in the chart below (and the red bars are “over65” deaths and blue bars are “under65” deaths). What might this mean? Again, I suspect it is the power of the vaccine to limit deaths in the over 65 community. I keep tracking this number and I hope that it doesn’t trend up again.

COVID Case Rates in heavy- and low-vaccinated States – 8/5/21

This may not be surprising at all, but the states with the lowest rates of vaccination are seeing case accelerations but the states with the highest rates of vaccinations are only seeing linear case rates. See below.

States with Lowest Vaccination Rates (as of 8/5/21)
States with Highest Vaccination Rates (as of 8/5/21)

I’m not sure what to make of the interesting spread in cases per 1000 across the 8 highest vaccinated states. Perhaps this makes the case that different approaches to state intervention yielded different results. New Mexico, for instance, had some of the more disruptive lockdowns and you can see that they flattened out earlier than New Jersey or Washington. But regardless, you’ll note that only a couple of these states have any case rate increase at all right now. However, the top chart shows states that have tended towards less government intervention and perhaps this is the reason their vaccination rates are low.

By County in AZ

I also see this result by county in Arizona. The highest vaccinated counties are all near the border (Yuma, Pima, Santa Cruz, Cochise) or near large Native reservations (Apache, Navajo, Coconino).

You’ll notice on the table and map below that these counties all have the lowest case rates and accelerations. In the map, the warmer colors represent higher case growth rates and the bubble diameter represents Zip code population. This shows the higher case rates are all in the counties with lower vaccination rates.

AZ State Data Table – 8/5/21
Arizona Zip Code COVID growth since April 2021.

Death Rates

I’m not including any slides on the death rates. They’re still low across the board compared with earlier outbreaks, but the states with lower vaccination rates do have slightly higher slopes, it seems.

Hospitalization (ICU beds)

# of ICU beds in use by COVID patients – 8/5/21 (

It’s hard to know what’s going on with the ICU bed usage rates… You may notice that for about a week the numbers have plateaued. This could be a data collection issue, or it could be that the hospitalization rate for ICU beds has slowed. I have noticed that COVID discharge rates seem very strong, so this might be a testament to hospitals improvements in treating serious COVID cases. I continue to track this metric.