How many have really been infected?

When I look at the different COVID-19 Case Fatality Rates (CFR), by country, and the fact that the number of new deaths per day is declining in most jurisdictions, I wonder whether many more people have been infected than we know about, meaning there is likely a greater degree of immunity than known.

Iceland has a CFR of 0.56%, Australia 1.39%, the US 6.02%, and the UK 14.21%.  CFRs are subject to many variables including the population demographics and the quality of the health system, so it is difficult to make comparisons between countries solely on the basis of the CFR.

We already know that many more people will have been infected than have been counted, because not everybody gets tested when they have symptoms and many people are asymptomatic.  It is also true that most testing is to see whether someone currently has COVID-19, not whether they have had the virus and recovered.

Terrigal dawn today (courtesy Julie)

But if we look at the countries with the highest per capita rate of testing, Iceland has done four times as many tests as Australia, the US and the UK.  My hypothesis is that if the CFR in the country that has done the most per capita tests (Iceland) is 0.56%, and we make the heroic assumption that the CFR rate should be the same across countries, then it stands to reason that the number of people who have been infected in a country such as the UK may well be twenty-five times the number reported, i.e., instead of 0.24M, it could be 6.2M.  In Australia, it would mean that instead of the 7,000 confirmed cases we have had nearer 20,000 cases.

Still sitting around getting fatter and more unfit.

I know this is a hugely simplistic analysis, but even if the numbers are not correct, it reinforces my impression that many more people have had COVID-19 than know about it.