The Mystery of Declining COVID-19 Mortality

by Brian T. Lynch, MSW

I want to point out a public health mystery regarding the COVID-19 virus that we can no longer ignore. The mortality rate seems to have dramatically declined from the initial wave in the Northeastern states back in March. Infections are resulting in fewer deaths in the second wave that has hit the Southern and Western states. What natural phenomenon can so profoundly alter the mortality rates so quickly?

Take a look at the two graphs of daily cases and daily COVID-19 deaths below. If the mortality rate remained the same, the basic shape of these two graphs should be nearly identical.

Instead, the early peak of new cases in the Northeast is much lower than the current second wave in the South and West, yet the peak in COVID deaths during the first wave is much bigger than in the current, much large wave of new cases. Has the virus mutated? Have medical interventions improved that dramatically? Or have reporting methodology changed the data collection to such a degree?

The two bar graphs above are the daily numbers of new cases on the left and daily deaths on the right over seven months. The blue and brown lines represent the 7-day moving average. Look at the differences in the peak averages of new cases and deaths between the April wave and the July/Aug wave we just experienced. When you calculate the differences, it turns out that the peak number of deaths in the initial wave back in April was 2 times higher than in the second wave in July/August even though the peak number of cases in the second wave was 2 times higher than in the initial wave. In other words, the second wave had twice the number of infections and half the number of deaths.

If this steep decline in the mortality rate of the virus is from mutations or improved treatments, rather than reporting issues unique to the United States, than similar declines in mortality over time should be evident around the world as well. This is something we should know, so here is the question:

QUESTION: Among the nations that have experienced a similarly higher second wave of COVID-19 cases as we have, does the United States stand alone in having a dramatic decline in mortality during the second wave of infections?

To answer this question, I looked for a sample of countries that had similar patterns of COVID-19 infection rates over time. Several countries had, or are having, a higher second wave of COVID-19 cases, including France, Japan and Sweden. The global pattern of the pandemic in general shows a similar pattern.

Next, I looked at the 7-day daily average of new cases and deaths for each of these countries and identified the highest daily average of new cases, and of deaths, for each wave peak in each country. I did the same for the global totals. I then calculated how much higher the peak number of average daily new cases was in the second wave versus the first wave. Likewise, I calculated how much higher the peak number of average daily deaths was in the first wave was than in the second wave of new cases. The results are summarized in the table below.

REDUCTIONS  IN MORTALITY BETWEEN FIRST AND SECOND WAVES OF CORONAVIRUS OUTBREAKS
Places w/Two Peaks	Daily New Case 7-Day Avg.	Daily Deaths 7-Day Avg.
	2nd Peak vs. 1st Peak	1st Peak vs. 2nd Peak
World	3.3 Times Higher	1.2 Times Higher
France	1.5 Times Higher	48.8 Times Higher
Japan	2.5 Times Higher	1.6 Times Higher
Sweden	1.7 Times Higher	4.0 Times Higher
U.S.A.	2.1 Times Higher	2.1 Times Higher

ANSWER: It seems clear that the lower mortality rate during a second higher wave of new cases over a period of time is a global phenomenon and not just something happening within the United States. While changes in how cases are reported may be a factor, it is unlikely that such changes are of primary significance. It also means that research is needed to understand why higher infection rates in a second wave of the pandemic produce lower mortality rates. The answer cannot be that the first wave simply killed off those with underlying conditions leaving healthier people to face the second wave. The second wave in the United States is primarily impacting an essentially different population with health characteristics identical to those people in the first wave. Clearly, the scientific community should focus some attention on this issue.

Below are the data graphs for average daily new cases and average daily deaths for the world, France, Japan, Sweden, and the United States. Note that in France, their second wave of COVID-19 infections has not yet produced a rise in the number of deaths despite the fact that there should be some evidence of this by now. And in Sweden, the death rate is on a long, slow decline, so I picked a data one month after the peak of new infections for the comparative calculation.