13 December 2021 Blog Post: Possible Omicron Signal in Los Angeles

Looking at the week over week smoothed incidence rate of COVID-19 infection in Los Angeles, we are now seeing a clear upwards trend in cases (Figure 1 below). Cases from 11/30/2021 to 12/.7/2021 increased from 8.9 cases per 100,000 population to 13.7 per 100,000 population.

To the left of the graph is included the Delta surge as reference. Notice first that we started from a much lower population rate for Delta (1.8-2.3 cases per 100,000 population) as compared to today (8.9-12.1 cases per 100,000 population). Current upward trajectory, however, seems to be about the same as it was at the beginning of the Delta surge (cases went from 3.2 to 5.7 to 11.4 to 18.4 to 24.0 and topped out at 32.4 – so a 10 fold increase). It is reasonable to assume that we are now in the midst of a combined tail-end of delta plus the beginning of Omicron in LA County.

Prevalence rates have not yet increased, but this is a lagging indicator as prevalence represents the number of active cases at a given time (distinct from incidence which is the number of new cases at a given time). Prevalence generally lags by about two weeks; the delta surge is included in Figure 2 below for reference.

Similarly, mortality (Figure 3 below) has not changed. It, too, is a lagging indicator for the impact of COVID-19. If preliminary reports about Omicron are accurate and should they similarly apply to Los Angeles County, then we would expect mostly mild disease from Omicron infections / reinfections.

A sharp increase in cases is not welcome news as we continue to be in a time of significant travel and holiday gatherings. While Omicron seems to be associated with more mild disease it nevertheless poses significant risk given enhanced transmissibility.Β 

𝗦𝗢𝗴𝗻 𝗨𝗽 𝗳𝗼𝗿 π—’π˜‚π—Ώ π—‘π—²π˜„π˜€π—Ήπ—²π˜π˜π—²π—Ώ

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