By Jerald Hughes
& Scott Robinson
The Third Wave of COVID-19 has been long and complicated. The shape of the two preceding waves followed standard epidemiological modeling, but the Third Wave exhibited both disruptions in data reporting and renewed surges, due to the holiday spreading events of Thanksgiving, Christmas, and New Year's Eve. This means that we saw illusory peaks shortly before Thanksgiving, and shortly before Christmas - but COVID-19 took off again after the holidays were over.
(The First Wave began in the middle of March and lasted about three weeks. The Second began mid-June and lasted a little less than twice that long. By comparison, the Third Wave has persisted more than 100 days at this point.) Now we might possibly be seeing a peak again. The most recent days' data have not increased. On the data from covidtracking.com, the recent highest 7-day average of new cases was 244,707 on Jan 11. The next two days declined slightly from that high.
The following chart shows the daily new cases since the Third Wave began on about Oct 7:
Chart: Third Wave Daily New Cases
The COVID-19 data often shows fluctuations in trends, even with 7-day smoothing. The number of new cases is the earliest available indicator - hospitalizations and death rates both lag cases by some period of days, so we cannot use those as confirmations.
One indicator that we can check is the positivity rate. Since positivity rate is the number of new daily cases divided by the number of total tests given, we must expect that the cases and rate measures will be closely related, regardless. The most we can hope for is to see a result which does not contradict the possibility that COVID-19 is peaking now. The chart below uses 7-day averages of these measures (positive tests divided by total tests), and does show a decline:
Chart: Positivity Rate
The number of total tests given has risen, after double-dip declines because of holiday data-gathering disruptions. If the positivity rate was level or climbing while the number of total tests increased, that would be a bad indicator. It is at least possible that COVID-19 spread is peaking now.
Chart: Total Tests
Deaths are a lagging indicator. Both the raw numbers of deaths and the fatality rates are currently at record levels. If the halt in the rise of cases described above really is a peak, then in about 10 days or so we should see daily deaths decline. If New Year's celebrations triggered COVID-19 spreading events, then by about Jan 11, ten days later, we should have clearly seen the effects of any surge in infections showing up in the data. Jan 10 through 12 were in fact the highest numbers observed in the 7-day average of daily new cases, so it can be at least hoped that whatever the negative effects that came from the New Year's holiday are, they have already been observed in the numbers, and hopefully we will not have more major spreading events occurring after Jan 1. One wild card that cannot be accounted for here is the danger of more highly infectious variants of COVID-19, which have caused new surges in the UK. These mutations have been observed in the US; how they will alter the course of the US's epidemic remains to be seen.
Jerald Hughes is Chair of the Department of Information Systems, University of Texas RGV. Scott Robinson is lead data scientist at Kentucky Farm Bureau Insurance.
All opinions expressed in this blog are solely those of the authors, and do not reflect those of University of Texas Rio Grande Valley, or any organizations of which either is a member.