VA COVID Status, Feb 16, 2021: positive news conitnues
VA COVID Status, Feb 16, 2021
Note: I am reporting on yesterday’s numbers. Life has gotten in the way of updating more regularly. I am continuing the monitor the numbers, and if the trends change, I will try to update. Otherwise, updates will be sporadic, as I need to tend to my health.
This 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.
Big picture: The numbers continue to improve. This is probably a result of returning to proper social distancing/hygiene after the holidays. The number of hospitalized continues to drop, and the percent positive is now below 10% again. All positive indicators. This cannot be explained by just vaccinations: that would reduce us from the beak by 10-15%, not 50%. So, good job, Virginia! Keep it up.
Yesterday’s case count is 1,770, our second consecutive day with under 2000 cases, the first time that has happened since mid-November. This is well over 1 standard deviation below the three-week bias-adjusted average of 3,278 cases.
The current weekly total of 19,192 new cases, or 2,742 cases per day, which works out to 42.0 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 1800, down by nearly half 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 an degrease at 3.3% per day or 21% per week.
Projection for tomorrow: 2143, with a 90% chance the numbers will be between:: 1570 - 2932
The testing numbers now show the percent positive to be about 2x the 5% metric over the last week (% positive 9.1%). 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 975,000 or so Virginians have received the first dose, and 300,000 have received both doses. This suggests that about 12% 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.
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, particularly in NOVA and SWVA, and NWVA, peaking in early to mid January. Since then, the case rate has dropped by more than half.
Looking at the weekly case count, we the see the numbers continue to decrease significantly, at 20% per week for the last 4 weeks (since mid January).
Regional growth rates (in fraction per day) continue to show decrease in cases 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.
Hampton Roads/Eastern VA
The entire state is increasing with Rt=0.967
The following table shows the number per 100K for each region. Again, NOVA and SW VA are doing the best, and the mountainous regions in NW & Central continue having more cases. However, all regions are improving over the last month.
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.
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.
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 peak value of 1700 cases per day. followed by a decrease to the current value of 665 cases per day.
City of Alexandria
Prince William Co.
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, we see we are once again in a downward trend in all NOVA counties, since the Mid-January peak, with the wealthier areas performing the best (less congestion?)
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, even though the numbers are less than half the mid-Jan peak. In Vienna, for example, we were under five in late September but are now at 25.6/100K/day.
Growth rate (%/day)
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.
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. When we look at W&M, for example, we see that the initial surge with some students carrying COVID to campus. However, the on-campus protocols seems to be working, and we the number of active cases are decreases at a rate faster than the state average. Quick looks Indicates the trend is true for most college towns -- at least those where the college numbers dominate the local down (exceptions include Lexington VA -- small college, mid-sized town).
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