VA COVID Status: Feb 6, 2021: Are we leveling off in our case decline?

 VA COVID Status: Feb 6, 2021

Today is full update

The introduction section, situation awareness, is updated with every post.  The figures and tables in the document are always updated, but the text in the remainder of the document is only changed as needed.


Situational Awareness

Big picture: The daily case count continues to decrease from the mid-January peak. While the daily counts have increased slightly but the weekly trends continue to show a significant improvement over prior week.  The number of patients continues to decrease from the peak, and the % of tests that are positive are down to around 11%.  I expect what has happened is the Dec – Jan increase was the results of people traveling for the holidays.  My expectations are that any further decrease will be a reflection of the number of non-immune people decrease due to the vaccination efforts.


Today’s case count is 4,709. which is in line with the three-week bias-adjusted average of 4,816 cases.


The current weekly total of 23,955 new cases, or 3,422 cases per day, which works out to 41.0 cases/day/100K people.  This is the lowest weekly total since right after thanksgiving (when we were seeing low numbers because of low testing over the long holiday weekend).    The number hospitalized is down to 2370, down 800 from the mid-January peak.  We continue to have capacity for 3000 more COVID cases in Virginia Hospitals, or about double the current numbers of COVID patients, and we will not exceed that in the near future.


The trends over the last three weeks now are showing a decrease at 3.2% per day or 20% per week.  


Projection for tomorrow: 3344, with a 90% chance the numbers will be between: 2471 - 4538


The testing numbers now show the percent positive to be about 3x the 5% metric over the last week (% positive 11.1%).  The 5% metric is often used to indicate sufficient testing. This is concerning because, as the percent positive increases, it is possible that some cases are being missed as the number of positives is constrained by the testing availability.  VA is tested about 2.2% of the population in the last week, down from 2.9% in the week prior to thanksgiving.  


Virginia is continuing to vaccinate group 1b; currently 780,000 or so Virginians have received the first dose, and 340,000 have received both doses.  This suggests that about 9% of the population have growing immunity, and 4% have nearly full immunity.  Most importantly, this group includes nearly all of the health care workers, mitigating the risk of a surge knocking out medical care.  As the numbers vaccinated increase, the number of cases should drop. With that said, there are reports out of South Africa that having a prior COVID exposure does not provide immunity to the new South African strain.  The vaccines, though appear to remain effective.  This means that our only chance for herd immunity is from the vaccine.


When we look at the local ZIP code data, we see that the observed increases are almost universal across VA. I am comparing the current estimated % positive to that of one month ago. Note that almost all is a warmer color (further from blue and closer to yellow). This is an indication of the uniformity of the increase. As a practical matter, it means to be safe and careful, no matter where in VA you live, there is risk.

 






 

Regions

In the spring, COVID-19 in VA was primarily a concern in the DC suburbs. Over three to four weeks, (from late May to early June), NOVA recovered and for about a month the disease was under control to the point that restrictions were eased. Unfortunately, in eastern VA/Hampton Roads, the easing of restrictions resulted in a surge in cases which peaked just before August 1st resulting in stricter restrictions in that area. Since then, with the exception of growth on college campuses, the disease has been stable, excluding the rural parts of the state where safeguards (social distancing and masks) are largely ignored. Starting in October our weekly case count has been increasing throughout the Commonwealth, peaking in mid January, followed by a steep decline.





Looking at the weekly case count, we see that the numbers are higher than at any other point in the pandemic.


Regional growth rates (in fraction per day) continue to show degradation over the past three weeks. Note: It is easier to show a decline when the prior numbers increased. The current growth rates for the different regions are shown below.


Region

Rt

NOVA

0.967

Central VA

0.969

Hampton Roads/Eastern VA

0.956

SW VA

0.959

NW VA

0.963


The entire state is increasing with Rt=0.9685


The following table shows the number per 100K for each region. Again, NOVA and Eastern VA are doing the best, and the mountainous regions in NW & SW continue having more cases. The concerning aspect is that in all regions the numbers for last week are significantly higher than the preceding three weeks. What is most concerning is that SW & NW VA are hitting significantly higher caseloads.

Daily Cases/100,000 

Region

Last month

Last week

NOVA

50.8

32.0

Eastern

70.2

46.4

Central

65.4

47.2

NW

58.6

59.6

SW

62.4

39.0


The following charts show all five regions of the Commonwealth over time.

The individual line charts show the unfiltered data per day, coupled with the trend lines. 


The trend lines show the different periods of growth.  


Early in the pandemic, the different parts of VA were functioning largely independently, with NOVA mimicking the northern states, and Hampton Roads mimicking the southern states. Since September 1, the regions have trended together. Starting in late September, NoVA and SWVA diverged from the rest of the state, a trend that continues today.


Currently SWVA has the greatest number of cases even though they have half the population of NOVA.  


Note that the effects at both ends of the chart are probably artifacts of the (seven-day polynomial filtering I use for averaging); the filter is poorly constrained in the first and last few days of the time history.  For those technically inclined, the filter is called a Savitzky-Golay filter, basically a moving window polynomial filter. At the edge (first and last days of the time series), the filter will over-compensate for the trend as it is unconstrained. I recommend the Wikipedia article if anyone is interested in more information, or contact me.


Also, I am aware that there is a glitch in the labels, and for some of the following charts, the final line is not included in the label.









Local/Northern VA:

After the early peak in May (~1,000 cases per day), NOVA saw a sharp drop in all COVID metrics, reaching a broad valley in mid-June (~200 cases/day), which lasted until around August 1st.  By Sept 1, NOVA increased to 300 but the caseload dropped to about 150 by late in the month. Since then we have had a steady increase averaging up to a a peak of 1500 cases per day before declining to current value of 807/cases per day.




Fairfax Co.

 0.968

Arlington Co.

 0.991

City of Alexandria

 0.966

Prince William Co.

 0.959

Loudoun Co.

 0.978

 

The Number above is Rt:  Rt is an exponential time constant, where the number of cases in a time segment is approximately, n=Ao Rt ^ t, where Ao is the number of cases at the start of the segment, Rt is the exponential growth rate, and t is the number of days since the start of the segment.  So, if Rt is greater than 1, it is growing exponentially, if it is less than one, it is decreasing each day.  


Another way to look at it, todays number are approximately the growth rate times yesterday's numbers.  This is the exponential time constant.  With time constants above 1, we are experiencing exponential growth in the case numbers.

Looking at the trends, the strong downward trend in daily case count we observed since around September 1st has ended.  We now see significant jump in cases in every jurisdiction.




The difference in the colors (contrast) in the NOVA map is increasing. In addition, the NOVA map is warming (as is happening throughout the Commonwealth). At this point, it seems likely that this is related to the fall surge others had predicted.  It is worth noting, though, that Vienna/Oakton is doing better than most of the region. 

 



 

Most localities in NOVA have case counts near or above 40/100K/day which is a dramatic increase since the fall.   In Vienna, for example, we were under five in late September but are now at 41.3/100K/day.

 

Region

Last month

Last week

Growth rate (%/day)

Fairfax County:

Vienna

40.8

23.6

-1.1

McLean

36.0

23.0

-1.1

S. Alexandria

54.1

33.4

 0.6

Reston/Herndon

39.5

29.0

-1.0

Annandale/Fall Church

56.2

31.2

-2.7

Fairfax

45.5

26.5

-3.8

Arlington/Alexandria:

 No. Arlington

34.8

27.9

 2.9

 So. Arlington

54.6

36.5

-2.7

 Alexandria

51.1

32.0

-0.3







Age Distribution: 

I am not updating this section for the time being except for the charts.  I will leave it here as is for a while longer--at times it can be very interesting.  This is particularly so when specific age groups do not follow other groups. For example, teens and 20-somethings surged in early September while the other age groups did not due to the outbreaks at colleges.

 



Colleges

I am no longer reporting on colleges in detail, as the college dashboards largely improved over the fall semester, and I think they are sufficient for reporting at this time.  In general, the readers are interested in the one or two specific colleges.  Googling “WM COVID Dashboard” for example will give the William & Mary COVID-19 dashboard, which has information more current than is available through other means.


With that said, the tends show increase in cases in all of the jurisdictions with colleges.  




 

Attribution:

1) You can repost/ share this information in its entirety by forwarding the entire link, or, 2) If you want to share partial content, you must receive my permission. This is proprietary information and I need to make sure you understand what I am saying. If anyone sees that this work being used without attribution, please let me know as soon as possible. I am willing to have an informed discussion/debate on my approach, but I want to make sure the proper context is captured.



Comments

  1. Hi David. It's been a while since your last post. Hope you are doing well and everything is okay. We all appreciate everything you do.

    ReplyDelete
    Replies
    1. I know I missed last week. I have limited energy and my return to work (1/2 time) has taken more energy then I expected. (I had been on disability since my cancer diagnosis). Rest assured, I am monitoring the numbers regularly, and nothing really has changed since my last update.

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