COVID-19 in Fairfax County VA, September 2021

An update for Sept. 17 is below.

Sept. 10, 2021: After 2 weeks of more data, it is time to update my Fairfax COVID tracker. The news is relatively good for Fairfax. Cases had been level around 170 cases per day (14.7 per 100,000) for the last couple of weeks and even had been trending downward slightly. The last 3 days have given a slight uptick but we will need to wait and see whether a new trend develops. Hospitalizations and deaths remain quite low with stable rates that remain around half of my model predictions based on last year’s pandemic (dotted lines). And Fairfax has much better rates for all three measures than the rest of the USA as a whole (see below).

Daily Cases (blue), Hospitalizations (green), and Death (red) in Fairfax County, Virginia, between July 1, 2021 (day 1) and Sept. 10, 2021 (day 72). The dashed line shows model predictions for a model developed between March 2020 and March 2021.

As for age, the number of cases in Fairfax among those under 18 continues to creep up. School has now been in session for 19 days here. The under 18 group represents 28 percent of the 748 cases total in the last 4 days. This represents an 87 percent increase in the case rate for this age group from its 15 percent of total cases over the last year and a half (13000 for under 18 out of 86000 total cases). By contrast, the number of recent cases in the 65+ age group is down by 30 percent from its pandemic average and is now only 7 percent of recent cases instead of the pandemic average of 10 percent of total cases. Thus, recent cases show a clear shift from older to younger. This shift is a likely factor in the decrease in hospitalization and death rates. The shift and decrease may also be due to the higher vaccination rate among older people and a lower rate among younger ones since most cases occur among the unvaccinated. Of the 14 COVID deaths in the last 4 weeks in Fairfax (ending Sept. 10), only 8, representing 57 percent, are for the 65+ group, whereas the pandemic average for this oldest group had been 82 percent of total deaths. I do not know the vaccination status of these 14 who died, but if data from elsewhere can be a guide, all of them, or maybe all but one, were likely unvaccinated.

To compare to elsewhere, the case rate per capita for the USA as a whole is 3 times higher than that of Fairfax and the death rate per capita is 8 times higher. The current death rate per capita in Florida is 26 times higher than for Fairfax and 3 times higher than for the USA as a whole. Florida is an outlier in these statistics–only Mississippi has a higher death rate per capita. Interestingly, Florida has a similar vaccination fraction to Fairfax (65 versus 67 percent for one dose or more). It does make a difference where you live. I am convinced that vaccination, masking, and other social practices have a big effect on the local course of this pandemic, which, in one way or another, affects everyone.


Update for Sept. 17: The counts for cases, hospitalizations and deaths continue to be relatively stable and steady in Fairfax, subject to the usual daily fluctuations. The graph below updates the previous one for Sept. 10. For the last 3 weeks the 14-day average number of cases has varied by plus or minus 10 cases around an average of 175 per day (15 cases per 100,000 population), and hospitalizations have averaged around 2.5 per day and deaths around 1 every 2 days, both remaining better than the predictions from my earlier model. All three rates remain much smaller than in most of the USA. There still is no evidence of a “school surge” in total cases (since cases are remaining flat 25 days after the start of school), although the case distribution tends to be younger with Delta than in the earlier pandemic. Since July 1, the under 18 age group has nearly doubled its fraction of cases, now up to 28 percent of total cases in the last 2 weeks; all other age groups have maintained or decreased their fraction of total cases relative to the pandemic prior to July 1. Of the 9 deaths in the last 3 weeks, 67 percent have been in the 65+ age group and the remaining 33 percent in the 18 to 64 age group.

Daily Cases (blue), Hospitalizations (green), and Death (red) in Fairfax County, Virginia, between July 1, 2021 (day 1) and Sept. 17, 2021 (day 79). The dashed line shows model predictions for a model developed between March 2020 and March 2021.

Depending on whether one takes the 1-, 2-, or 3-week average for the COVID death rate per capita in Fairfax, one gets a rate that is from 30 to 40 times smaller than the current per capita COVID-19 death rate in Florida. As for other recent weeks, Fairfax remains much better in this regard than much of the rest of the country. This raises the natural question: why is there such an enormous disparity in this crucial measure in different parts of the country? And why is Fairfax doing so well? I address this in my post on August 19.