As very many do, I have been trying to form my own personal, data driven, opinion on the evolution of the SARS-CoV-2 pandemic; or the Covid-19 pandemic. Is it tapering off? Or will it last a decade? Or, most importantly, what does data tell us?

I used the Covid-19 Tracking Project data. It is reasonably clean, and it is easier to deal with than raw data from the Center for Disease Control and Prevention. The Covid-19 Tracking Project collects and aggregates data at the state and national level, scraping state health department websites, twitter accounts, and jotting down data from state health department press conferences.

I look at US national aggregates, as they smooth off differences among states. Aggregating over an estimated population of 331,002,651 (expected US population in 2020) should lead to quite robust, if any, conclusions.

Let’s look at daily deaths, newly detected positives and hospitalizations, per day:

The raw data in Figure 1 does not say much. Some states do not publish data on their healthcare website during weekends, hence the periodicity. Weekend data becomes available the following Monday, or Tuesday, which causes the big spikes.

Also, the magnitude of new positive cases dwarfs and flattens the hospitalized patients and deaths series.

As mentioned in another post, the Case Fatality Rate (CFR) measures the lethality of diseases in a unit of time. Let’s focus on positives and deaths, to measure the crude daily CFR for Covid-19 in the US.

In Figure 2, I have scaled the deaths series up by a factor of 45, in order to be able to compare the two series. Obviously, there have never been 100,000 deaths per day in the US, and hopefully there will never be. At a rough observation, it seems that for the past year, deaths peaked about 14 days after the new daily positives peak. It is easier to see, by smoothing both series via a 7-day moving average.

In Figure 3, both the daily deaths series and the daily new positives series have been smoothed by a 7-day moving average. The daily deaths are scaled by a factor of 45 as I described above. In the spring and summer peaks, there was a lag of 14 days between the peaks of positives and the peaks of deaths. The distance between the vertical blue line (new daily positives peak) and the vertical red line (daily deaths peak) is exactly 14 days. This is a widely accepted fact among epidemiologists in the USA. For US data, deaths lag new positives by approximately 14 days. We can register the two series by lagging deaths back by that amount.

In Figure 4, note that both the moving average and the lagging back of deaths remove data points at the end of the series. The above graphs were generated on November 17, 2020; the combined effect of the moving average and lagging back removes approximately 18 days from the end of the graph. Thus, daily CFR calculations lag back in time by 18 days.

We are now ready to calculate the daily crude CFR for the past 10 months, the ratio of deaths (lagged back by 14 days) to new positive cases.

Figure 5 needs interpretation. Covid-19 never had a CFR of 50%. The CFR peak in March is due to lack of widely available tests. The number of positives, in that time frame, was extremely under-estimated. As Covid-19 tests became widely available, the daily crude CFR started to settle toward the real crude CFR.

This is a crude, un-adjusted, CFR, as the number of positives does not measure correctly the true number of positives. We know for sure that there are people who became infected, without even noticing it. Some were infected and suffered minor symptoms, but, they never sought testing. The adjustment factor to transform crude CFR into adjusted CFR varies from state to state. New Mexico estimates its own adjustment factor to be 3.2. Other states go as low as 3, or as high as 6. High density of population states tend to use an adjustment factor of 6 or higher. We will use a national average of 4.5, which will come in handy later on.

One could think of the daily crude CFR as the individual probability of dying, once an individual tested positive, averaged over all ages, 14 days after testing positive.

Let’s zoom on recent months, eliminating the March artifact.

In Figure 6, the red line is the daily crude CFR. The blue line is a LOESS local regression curve fitting, to highlight the trend. The drop from April to July is still likely an artifact due to the progressively increased availability of test. Around July, the crude daily CFR settled around 1.7% – 1.5%. The 1.5% figure has been widely popularized in classic and social media as the “mortality” of the Covid-19 pandemic. In reality, mortality is a whole different quantity. We will not be able to compute the true mortality rate of the Covid-19 pandemic until January 1st, 2021 at 00:00:01. The crude CFR rate of 1.5% turns into an adjusted CFR of 0.33% (using the national average 4.5 adjustment factor – adjusting for unaccounted, untested positives); the Covid-19 CFR is about 3 times higher than the accepted adjusted CFR of the common flu, which clocks at 0.1%.

Comparing the 1.5% crude CFR of the Covid-19 pandemic to the 0.1% adjusted CFR of the common flu, as many do in the media, amounts to comparing oranges and apples.

Also, we notice that, in October 2020, the CFR appears to be decreasing steadily. Let’s focus on that.

Undeniably, for the month of October 2020, daily crude CFR has been decreasing steadily. This is the result of a massive increase in new positive individuals, not matched by a comparable increase in deaths (or hospitalizations, for the matter)

What would happen, if the CFR current decreasing trend would steadily continue through November, December and January? Here’s the answer.

Figure 8 is a busy graph. Let’s go through it in detail. The y-axis is expressed in units of adjusted CFR, not crude CFR, as previous graphs had. Observed crude CFR for Covid-19 has been adjusted using the 4.5 factor, as discussed above. The red line is the observed CFR for the month of October. The horizontal purple line is the adjusted CFR for common flu. The green line is a fitted linear model to the observed adjusted CFR, extrapolated through January.

If the observed CFR were to maintain the October 2020 trend through January 2021, Covid-19 would reach the same level of lethality of the common flu, marking the end of the pandemic. The blue line indicates the approximate date when the Covid-19 adjusted CFR would reach the level of adjusted CFR of common flu: approximately January 21, 2021.

Can I offer any guarantee that the pandemic will end on January 21, 2021, on the dot? Absolutely not. As I am writing this, the “second wave” is starting, and it might push back that date. Likely, the CFR will not decrease linearly, but it will follow an exponential decay function, with a very long tail: there will still be sporadic cases and, unfortunately, deaths well into the summer and fall of 2021.

The availability of therapies (remdesivir, convalescent plasma, monoclonal antibodies) might expand the time between the peak of new positive cases and the peak of deaths in the second wave, beyond previously seen 14 days: in this case, the model would be different. The date when the CFR of Covid-19 will match the common flu CFR might be further pushed back. Come back to this blog in early December, we will look at the November data.

Am I suggesting that the pandemic is almost over, and you should refuse the vaccine, if offered one? Absolutely not. If offered a vaccine, we should all accept it. Two main reasons:

1. The possibility of a new future Coronavirus pandemic is real. It is possible that the new future Coronavirus will be antigenically similar to the SARS-CoV-2. I am personally convinced that those, who had SARS-CoV-2 with minimal or no symptoms, had one or more previous encounters with antigenically similar Coronavirus, perhaps with a mutated SARS-CoV-1.
2. There will be SARS-CoV-2 endemic pockets and sporadic cases throughout 2021. You do not want to be one of those.

I am offering here a glimmer of hope. The Cassandras of Doom and Gloom, who predict we will be in lock down in 2022, should look at data and change their tune. The SARS-CoV-2 is at a constant mutation rate.

Sometime in the Spring of 2021, we will be able to return to our lives.