An Omicron oddity: The number of cases doesn’t predict the number of deaths

Early in the Covid-19 pandemic, the case fatality rate was frightening. This metric represents the proportion of all known people infected with a disease who die from it. The World Health Organization initially put it as high as nearly 16% in Algeria.

Several colleagues and I at Vital Transformation began closely following the data on Covid-19 early in the pandemic. We wondered if case fatality rates might be skewed by lack of testing. We collected data on various indictors that early on were thought to be influencing the spread of Covid-19.

We analyzed standard metrics such as case rates weighted by age and population densities, but also deeper metrics such as tourists per year and the number of university students in a city. Our findings, published in April 2020, showed that the case fatality rate was indeed being widely overstated and predicted that it would drop by 5% for every 10% increase in the number of tests.

That prediction turned out to be correct, as it is now known that the majority of early Covid-19 cases, particularly in those under age 65, had been completely missed. The overall infection fatality rate, the actual measure of deaths due to the overall rate of infection across the entire population obtained via genetic testing, is closer to 0.2%, or two deaths per every thousand people infected.

Since that time, we’ve kept a keen eye on the relationship between cases and deaths, particularly during the recent waves, which have been influenced by improved treatments and vaccines, as well as by new variants. There are legitimate concerns about the trajectory of the newest variant, Omicron, and public health experts are paying close attention to the exponentially mounting cases, particularly in the United Kingdom, which in the past has functioned as a canary in the Covid-19 coal mine for the U.S.

While early reports from South Africa suggested that Omicron might cause less-severe Covid-19, the rapidly mounting case numbers and overall transmissibility have been alarming, particularly in the U.K. According to a Dec. 10 government technical briefing (see page 17), Omicron cases were expanding by 35% per day.

But there’s something else different this time around, at least in the U.K.: the statistical relationship between Covid-19 cases and deaths appears to have broken down with Omicron.

Looking at daily death rates in the U.K. from May 15 — essentially from the point at which the Delta wave began — to Sept. 15, there is a highly statistically significant relationship between daily new cases and deaths. In short, case rates accurately predict death rates.

But beginning the analysis on Sept. 15, coinciding with flattening of the Delta curve and the onset of Omicron, shows no statistical relationship between Covid-19 case rates and deaths.

In earlier waves, rising death rates would follow an increase in cases; the impact of rising cases on death rates could be seen visually and validated statistically. Deaths would follow cases upward, and peak roughly two to three weeks after new cases began trending downward. With Omicron, however, we not only don’t see the rise in death rates that were associated with the first waves, but we actually see a continuing decline in death rates, despite a radical increase in cases.

Whether or not this breakdown of the relationship between Omicron cases and deaths will play out in other countries, like the U.S., is hard to say. Omicron is currently more prevalent in the U.K. than in the U.S., and the U.K. has far better screening rates, both of which could alter the outcome in the U.S.

It’s still, of course, early days. While it is possible that death rates due to Omicron may rise later, at the moment in the U.K., Covid-19 daily cases no longer meaningfully link to deaths. So, according to the math, Omicron cases rising no longer automatically means impending doom and gloom, nor does it require apocalyptic language like we’re hearing from the media and political leaders implying mass waves of death with rapidly increasing case rates.

Let’s hope these statistics hold.

Duane Schulthess is the managing director of Vital Transformation, a Belgium and Washington, D.C.-based health consultancy firm. This article was written with input from Harry P. Bowen, economics research partner at Vital Transformation.