The graph shows the status of Covid-19 in Fairfax County Virginia at the end of March, 2022 (see Section below for an analysis given at the beginning of March). Cases C have leveled off around 100 cases per day, and may be showing a slight increase near the end of March. Daily hospitalizations H have been tracking the new rate of 1 H for every 380 cases (153 H out of 59133 total C so far in 2022), with the exception of an unusual spike in early March. The H data for February and March have shown both the spike and a large subtraction in previously recorded cases, so this later data after the Omicron peak in January may reflect the addition or subtraction of earlier hospitalizations as VDH re-evaluated earlier data to ensure accuracy. In any case, the current (March 31) average H rate of around 1 H per day seems a bit high compared to current cases. It is very clear that deaths D have tended to peak around 5 weeks after case onset. Oddly, the death rate that accounts for the data in February and March corresponds to around 1 death for every 270 cases (222 deaths out of 59133 cases in 2022). This is not as good a death rate at it appeared in January, where most deaths from Omicron variant had not yet occurred because of the 5 week average delay between onset and death. The current death rate is also around 1 per day in Fairfax County. Oddly, the number of deaths in 2022 have exceeded the number of reported hospitalizations. The death and hospitalization rates in Fairfax both remain relatively low now, around 1 per day, subject to statistical variation. I do not know to what extent the current H and D reports reflect updating and correcting earlier data; this seems to be ongoing, since some days report negative H events due to removal of earlier events.
Fairfax no longer reports cases by age group, but continues to report deaths by age group. The percentages are: 0 -17 (0%), 18-49 (6%), 50-64% (13%), and 65+ (81%). The high fraction for the oldest age group is consistent with the percentage throughout the pandemic since March 2020.
Beginning of March, 2022
The graph shows the status of Covid-19 in Fairfax County Virginia at the start of March, 2022. Cases have rapidly dropped exponentially since their peak in mid-January with a half-life of around 8 days, a little slower than the ramp-up doubling time in December. Case rates are now comparable to what they were in late November before the ramp-up due to the Omicron variant, namely around 120 new cases per day. The low hospitalization and death rates during the recent surge are discussed below the graph. The hospitalization rate is around 5 times lower than during the Delta surge in the summer/fall of 2021, but oddly, the death rate remains about the same as before.
Cases started to rise in early December 2021, peaked in mid-January 2022, and declined steadily through February 2022. Hospitalizations followed cases throughout the surge by the formula H = C/380, as seen in the bold and light green lines in the lower panel of the graph. This is a 5.4 times lower hospitalization rate per case than in the Delta surge in the fall of 2021. The VDH had announced that it was implementing a new national policy on reporting Covid-19 deaths starting on Jan. 1, 2022, and there would be a delay in reporting during January. I presume that partially accounts for the delay in death until February, during which there was a rapid rise and peaking of reported deaths. A very low number of deaths were reported in January and they spiked around day 222, Feb. 7. The thin red line shows the predicted number of deaths, assuming a delay of 5 weeks between case onset and death and assuming the prior death rate for the Delta surge, 1 death for every 360 cases. This qualitatively accounts for the total number of deaths in Fairfax in 2022 and the delay; statistical variation and model errors make it hard to be quantitative. The delay may be real rather than an administrative one with delayed reporting since there is a similar 4-week delay between case onset and death in the national data for the Omicron surge for all of the USA. Previously the delay between onset and death was closer to 2 weeks. The change may reflect the nature of Omicron in contrast to earlier variants.
The actual data for Fairfax County from January 1 through February 28, 2022, are the following: 57538 cases, 87 hospitalizations, and 169 reported deaths. There were actually 152 hospitalizations reported, but 65 hospitalizations were removed, resulting in negative counts some days. VDH did not say whether the removals reflect hospitalizations reported in 2022 or prior ones from 2021. The January peak in hospitalizations in the graph reflects the daily 2022 report, since the data removal was in February only. The 152 hospitalizations correspond to 1 in every 380 cases, whereas 65 corresponds to 1 in every 660 cases. The 169 deaths correspond to 1 in every 340 cases. It is odd that there were more deaths reported than hospitalizations, although everyone who died may not have been hospitalized. Cases in 2022 represent 32 percent of total cases (172659) since March 2020, whereas deaths in 2022 represent only 12 percent of the total number of Covid-19 deaths (1370) in Fairfax since March 2020.
Fairfax has stopped reporting cases by age group. Before they stopped reporting, around 80 percent of cases were among the under 50 age group, and only around 5 percent in the 65 and older group. Fairfax continues to report deaths by age group. As of Feb. 28, the 169 deaths in 2022 are distributed as follows: none for under age 18, 5 percent for age 18-49, 12 percent for age 50-64, and 83 percent for age 65 and over. Thus, the most cases in the recent surge have been for those under 50, and the most deaths for those 65 and over.
All of the above numbers primarily reflect the situation for unvaccinated people, since state data show that nearly 80 percent of all cases in Virginia are among unvaccinated people, representing around 15 to 25 percent of the population (75 percent of Virginians were vaccinated at the start of the surge, 85 percent now). Vaccinated people can expect the corresponding C, H, and D rates to be several times better than these overall numbers for the entire population. But I have not carried out a specific analysis of that. But according to state data for all of Virginia, during the January 2022 peak of the recent surge, unvaccinated people were 20 times more likely to be infected and 10 times more likely to die than fully vaccinated people. The message is clear: vaccination is one of the simplest, most effective, and safest ways to minimize the effect of the pandemic, and save lives and needless suffering.
Finally, the data for the last week suggest a leveling off of the drop in cases, perhaps even an increase starting again. We will need to watch this as more disease-fighting measures come off
Word and Fire 