COVID19 update, October 4, 2020: age dependence of infection fatality rate; how this explains why the second wave is much less deadly than the first; new respect for Sweden from.. the NYT?!

(1) Via Dr. Seheult (video here) and Dr. Campbell (video here), a preprint of a meta-analysis (in plain English: a distillation of statistical data from many primary studies) that finds a surprisingly simple “rule of thumb” relationship between infection fatality rate and age:

%IFR=exp( -7.53 + 0.119*age_in_years)=10^(-3.27 + 0.0517*age_in_years)

Image may contain: text that says 'Figure 3: The log-linear relationship between IFR and age 5 2.5 Meta-Regression Confidence Interval Prediction Interval Logarithm of IFR Representative Sample Convenience Sample Comprehensive Tracing -2.5 80 -5- -7.5 10 20 30 40 50 60 70 80 90'
Confusingly, the Y axis is natural logarithms (base e), not common logarithms (base 10)

A money quote from the abstract: “We find that differences in the age structure of the population and the age-specific prevalence of COVID-19 explain nearly 90% of the geographical variation in population IFR.”

(2) On a related note, Dr. Seheult also points to a very detailed data page on the website of the ECDC (the European Centers for Disease Control). One very telling set of graphs is an age breakdown of the per-capita infection rate, when juxtaposed with the graphs of overall infection and fatality rates. For example, below for Belgium:

Note that the 1st wave is dominated by age 80 and over (the darkest line), while the 2nd wave is predominantly young people

As a result, below you see a shark peak in mortality in the first wave, while the rise in infections in the second wave is not accompanied by any significant rise in mortality (yet). Wishful thinking about “the virus getting weaker” need not be invoked, as the exponential dependence of infection fatality rate on age is more than adequate to explain the variation.

But don’t take my word for it: have a look at the corresponding graphs for the other countries. Here, for example, is Germany, more meticulous in data curation than most:

(3) The end times must be upon us, because the New York Times, which has been excoriating Sweden in shrill tones for its “road alone” in handling the COVID19 epidemic, just published an article about Sweden that is surprisingly fair: “Vilified Early Over Lax Virus Strategy, Sweden Seems to Have Scourge Controlled. After having weathered high death rates when it resisted a lockdown in the spring, Sweden now has one of Europe’s lowest rates of daily new cases. Whether that is an aberration remains to be seen.” ( Archive copy here: https://archive.is/99o2J )They even go as far as to say:

In response to the recent outbreaks, many European countries are imposing new restrictions. But political leaders, anxious to avoid unpopular and economically disastrous lockdowns, are relying mostly on social-distancing measures, while trying to preserve a degree of normalcy, with schools, shops, restaurants and even bars open. In essence, some experts say, they are quietly adopting the Swedish approach. “Today, all of the European countries are more or less following the Swedish model, combined with the testing, tracing and quarantine procedures the Germans have introduced, but none will admit it,” said Antoine Flahault, director of the Institute of Global Health, in Geneva. “Instead, they made a caricature out of the Swedish strategy. Almost everyone has called it inhumane and a failure.”

I remember thinking that Israel, under new COVID19 czar Roni Gamzu, had adopted a “modified Swedish model” for the second wave, until we were blindsided by steep rises in infections in two minority sectors of the population, and a second lockdown was declared in response to hospitals in affected areas approaching capacity limits.

Is Sweden approaching higher-order herd immunity? Or has the virus just run out of ‘low-hanging fruit’? Or is it merely between two waves? Public health chief Dr. Anders Tegnell addresses the question:

Mr. Tegnell stressed, as he has many times before, that Sweden did not set out to achieve “herd immunity,” calling it a “myth that has been created.” “We are happy that the number of cases is going down rapidly and we do believe immunity in the population has something to do with that,” he said in the interview, conducted just before the case numbers rose slightly. “And we hope that the immunity in the population will help us get thought this fall with cases at a low level.”

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