This is how I see the U.S.A today. Starting from the bottom of the legend, the bright red states all had a high rate of new COVID-19 cases and a very sharp peak rate that occurred in late November. Moving to the other end, almost all the East Coast and West Coast states have similar low upward trends in new cases.
What I find so interesting is how nicely geographically clustered this looks.
- Everything in north-central part of the country peaked late last month.
- That’s ringed with non-coastal states that have a high current trend.
- Wheras almost all the coastal states (except Rhode Island) have low upward trends (currently under 40 new cases/100,000/day.) or moderate upward trends (40 to 60 new cases/100,00.day).
Details follow.
States by Census Region and Division
The graph above shows the seven-day moving average of new COVID-19 cases per 100,000 population per day, for U.S. states. As rates have risen across the U.S., a handful of states have fallen behind the pack. And, thankfully, Virginia (thick black line) is one of those. At this point, only Vermont, Maine, and Hawaii have lower rates than Virginia.
At the other end of the spectrum, North Dakota showed a sharp peak in its rate of new cases, late last month, and is no longer leading the pack. Five states (MN, SD, NE, WY and RI) currently have have new case rates that modestly exceed that of North Dakota.
Let me now break that down by Census division.
Source: National Center for Health Statistics (US). Health, United States, 2018 [Internet]. Hyattsville (MD): National Center for Health Statistics (US); 2019. Figure, U.S. Census Bureau: Four geographic regions and nine divisions of the United States. Available from: https://www.ncbi.nlm.nih.gov/books/NBK551093/figure/appii.fig1/
Above: The three West Coast states (CA, OR, WA) show virtually identical trends (middle three lines above.). Alaska and Hawaii (high outlier and low outlier above) are on this chart because that’s how Census classifies them, geographically. But they otherwise have nothing to do with the three West Coast states.
Above: Almost the entire South Atlantic Census Division shows trends similar to those on the West Coast. Geographically, the high outliers here (DE, WV) are on the fringe of the Division. Delaware has much in common with New Jersey and states farther north, and West Virginia has more in common with the mountainous parts of the East South Central states.
If we were to add CA, OR, WA to this graph above, you wouldn’t be able to tell their trends separate from those of the South Atlantic states.
Above: New England and Mid-Atlantic states span a much broader range of new case rates, but show the same general shape as all the states above. There has been a broad, moderate rise in new case rates, and no evidence clear peak yet. Rhode Island is an unexplained high outlier. Maine and Vermont are the low-lowers, and have pretty much been doing their own thing, separate from the rest of the country, since the start of the pandemic.
Above: Trends in the South Central states are a bit more spread out and diverse, but still show the same general shape. A broad rise — to generally higher levels then the states above — with no clear peak yet.
Above, both graphs: The Mountain and Midwest (North Central) states are where all the highest rates occurred in recent weeks. In both regions, almost all the states appear to have hit some sort of peak (at least in the short run) except for the states with the lowest rates of new cases. There (AZ for the Mountain states, OH for the Midwest states) rates continue to increase slowly.
If I then broadly characterize states into six groups, I get the map at the top of this posting.
- Sharp peak. These are states with lines that look like North Dakota’s. Most (all?) have a peak in excess of 100 new cases/100,000/day.
- Broad peak. States that appear to have peaked in the last two weeks, but with a much broader, shallower peak. These all peaked below 100 new cases/100,000/day.
- High trend. States where new cases are still trending upward, with current rates above 60/100,000.day.
- Moderate trend. Same as above, but 40 to 60 / 100,000/day.
- Low trend. Same as above, but under 40 / 100,000/day.
- Independent — Hawaii, Alaska, Maine and Vermont are either geographically isolated, or have shown no relationship to surrounding states since the start of the pandemic. These areas appear more-or-less independent of the rest of the U.S.
Different drivers?
You can’t help but guess that whatever drove the U.S. third wave in the north central states has to be somewhat different from the current drivers on both coasts.
Source: New York Times. For sure, propensity to wear masks is quite different, with the north central states showing (late summer) mask use at the lowest rates in the nation.
But you still have to think that one or more other common factors may be at play as well. The slow rise on both coasts looks like the slow decline in population vitamin D levels as winter sets in (one factor thought to contribute to wintertime flu season). Or possibly the small increase in indoor time that occurs for US adults in wintertime. (Both of which were documented in earlier posts.)
But the skyrocketing rates in the north central states, followed by sharp turnarounds, suggests a different causation entirely. And the question remains, is that sort of thing going to happen everywhere? Does the continued upward trend in the east and west coast states mean that we are all going to end up looking like those north central states, sooner or later? Or were those extreme and sharp peaks somehow unique to that area, and will not be repeated as the third U.S. wave of the pandemic progresses.
I’m still betting that the main driver of the wintertime flu peak is low indoor humidity. And that this will also be the driver of the wintertime peak in COVID-19. If so, we’re going to test that out a few weeks from now, in Virginia, as the impact of colder, dryer weather makes its way into the COVID-19 case counts.
