Hopeless

  

Congressman Tom McClintock (California 4th district) advanced the following theory today on a call with his constituents. The reason, he suggested, that America was doing so poorly in the battle with covid-19 is that we didn't reopen fast enough. He cited Sweden as an example of a country that opened quickly and has suffered way fewer deaths. Why? The congressman asserted confidently that it was because Sweden has achieved herd immunity.

Let unpack that a little, as it seems a fairly bold claim. Since there is no vaccine, to achieve herd immunity, depending how contagious an infection is, 70% to 90% of a population needs to have contracted the disease^[1]. Since this is a highly contagious virus, we should probably use the higher number, but for the moment let's use the middle figure, 80%.

Sweden's population in 2019 was about 10 million, so 8 million people would have had to have contracted the disease for Sweden to have herd immunity as the congressman suggested. The congressman also maintained that the number of reported cases was not a good metric and that he relied on mortality as a reliable indicator. So let's do that.

The covid-19 mortality rate is widely believed to be about 0.6%, although Johns Hopkins data^[2] suggests the rate may be much higher, around 2%. Worldwide the death rate of confirmed covid-19 cases is 3.8% (if we exclude the UK which clearly has't got it's act together either, the morality among confirmed cases is still 3.6%).

Let's start with this figure; 3.6% of 8 million is about 290 thousand deaths. But Sweden has reported only 5,743 deaths, significantly lower.

If we use the 3.6% mortality rate to impute the number of cases, that gives 160 thousand or 1.5% of the population - nowhere near the 80% needed for herd immunity. If we use the lower mortality rate of 2%, that would imply an infection density of about 2.8%. And if we use the 0.6% figure, we get just 9.3%.

Only if we assume that covid-19 is about 30% less lethal than the flu do we get to a number that approaches the 80% herd immunity number.  By the way, Sweden also reports only 80 thousand cases, not 8 million.

So Congressman Tom McClintock's claim that Sweden has achieved herd immunity seems fanciful at best and illustrates why one should listen to well informed experts rather than ill-informed (or less charitably, malevolent) politicians.

^[1] https://www.jhsph.edu/covid-19/articles/achieving-herd-immunity-with-covid19.html

^[2] https://coronavirus.jhu.edu/data/mortality