Covid-19 in Fairfax County, Virginia, October 2022

A new model

This time I am introducing a new model to analyze the recent Covid-19 data from Fairfax County VA. The reason is that it appears that cases have been seriously undercounted since last spring. The data driving this conclusion is the relatively high hospitalization rate over this time frame, namely an average of around 3 or 4 hospitalizations per day over most of this time, now averaging around 2 per day). This forces one of two conclusions: either (2) cases have become more significantly undercounted since the widespread availability of home test kits, or (2) the disease has become significantly more virulent, resulting in more people getting very sick requiring hospitalizations. Since there is no evidence elsewhere of the second possibility, and since the first possibility of a higher level of undercounting is quite plausible, in order to account for the data, my new model assumes that cases have been undercounted fourfold since May. The new model assumes assumes a hospitalization rate of 1 per every 350 cases, essentially unchanged from the rate from the winter Omicron surge. But now the model counts the number of cases by multiplying by 4 the REPORTED number of cases, based on positive PCR tests. Consequently, by keeping the hospitalization to case ratio fixed near its prior value, the new model estimates that 75 per cent of actual cases remain uncounted by PCR tests reported to the state.

With the above assumption, the relatively low death rate of around 1 per day in Fairfax County is explained by assuming a new death rate of one death in 1000 cases. If the model assumption regarding cases is correct, this death rate represents a significant improvement over the one that applied earlier during the Delta and Omicron surges.

The numbers in the graphs below use these new model assumptions. The light dashed lines for daily hospitalizations and deaths show the predictions of the model, which more or less track the data within statistical variation and with some inevitable model errors. The implication for cases is that the actual number of cases remains quite high. To put it in perspective, we may have had nearer to 200,000 cases in Fairfax County since May 1 instead of the reported 54,000 cases. That would mean 1 in every 5 persons in the County would have had Covid-19 in the last 5 months. The pandemic is NOT over–sorry, Mr. President.

October 1 2022. The points show daily case (blue), hospitalization (green), and death (red) data for Covid-19 in Fairfax County, Virginia, between April (day 120), and July 31, 2022 (day 396); source: Virginia Department of Health, VDH. The case numbers here MULTIPLY BY 4 the reported cases confirmed by reliable PCR tests; this provides an estimate of untested or home-tested cases based on assuming an unchanged hospitalization rate from earlier data before home testing was widely available. The solid blue, green and red lines show 7-day average data. The light green and red lines show my model predictions, assuming a hospitalization rate of 1 in every 350 cases and a death rate of 1 in every 1000 cases, delayed by 5 weeks (35 days) from case onset.

If I did NOT make the assumption of undercounted cases, explaining the reported number of daily hospitalizations and deaths would allow me to assume the same death rate as for Delta and Omicron (1 in 270 case) but with a hospitalization rate that is 4 times LARGER than during Delta and Omicron. While I can not rule out this possibility, I believe it to be a more reasonable assumption to assume that there is a large four-fold undercounting of cases due to many home tests and untested cases. If I am right, there is now a large number of cases in circulation in Fairfax, over 500 per day, but the impact on most individuals and the medical system is slight because cases are normally not causing serious illness that leads to hospitalization or death. An alternative (but unlikely) possible interpretation of the data would be that cases remain low (at the reported level), but the disease causes a much higher rate of hospitalization than before.


Fairfax County lists Covid-19 deaths by age group: in the 153 days between May 1 and Oct. 1, 2022, 8 people under ager 65 died and 129 people 65 and older. Thus, 94 per cent of the total deaths were among those 65+. Virginia state data indicates that most of those who died were actually 80 and older. If one is 80+ and gets Covid-19, the odds of dying are 1 in 24 cases according to state data. This improves to closer to 1 in 100 cases for someone 65 to 80, and better than 1 in 1000 for those under 50. Most of the people who die are among our oldest citizens. Virginia no longer reports case and death data according to vaccination status, but the national data for recent weeks show that the odds of dying from Covid-19 are 6 times higher for the unvaccinated than the vaccinated. As before, it remains true that most of those getting seriously ill or dying from Covid-19 are unvaccinated elderly people. Vaccination still offers a major improvement in one’s odds of surviving a bout of Covid-19, irrespective of age.