Western Europe has suffered a recent upsurge in coronavirus infections after having suppressed the initial spike. The US, far less successful in quelling the first wave, continues to record hundreds of covid deaths daily. Still, extrapolating from international seroprevalence surveys, these countries’ estimated cumulative infection rates remain under ten percent — far below the seventy percent widely regarded as the threshold for achieving herd immunity. Are there countries whose infection rates place them closer to the magic number?
Granted, data on deaths and their causes are unreliable in many parts of the world. Still, death rates are more reliable than diagnostic test-positive case counts, which vary widely based on availability and selection criteria. As a gross approximation, here’s an algorithm for estimating a country’s cumulative covid infection rate based on death rate:
- Retrieve the nation’s cumulative covid death count per million population.
- Retrieve the nation’s median age.
- Estimate that nation’s covid fatality rate. For the US I’ve been using 0.85%, but that percentage must be age-adjusted because older people are more likely to die of covid infection. The median age of the US population is 38 years. Here’s the quick-and-dirty age adjuster I’ve been using that fairly closely approximates international seroprevalence results:
- For countries with a median age above 38, multiply 0.85% by 1.1 to the power of years in excess of 38. E.g., if a country’s median age is 42, the estimated fatality rate is 0.85 x 1.14, or 1.24%.
- If a country’s median age is below 38, divide 0.85% by 1.1 to the power of years under 38. E.g., if a country’s median age is 30, the estimated fatality rate is 0.85/1.18, or 0.40%.
- Multiply death count per million by estimated fatality rate, then multiply that product by 100,000 to arrive at the percentage of the country’s population infected by covid. (Deaths lag infections by about 3 weeks, so the algo estimates cumulative infections as of early September.)
As of 26 September, the countries with estimated covid infection rates of at least ten percent are:
- Bolivia = 30 percent
- Peru = 30 percent
- Ecuador = 19 percent
- Mexico = 18 percent
- Panama = 15 percent
- Iraq = 14 percent
- Brazil = 13 percent
- Colombia = 13 percent
- Chile = 11 percent
- Honduras = 11 percent
- Guatemala = 10 percent
Latin America clearly dominates the list. Not one of these countries is even halfway to herd immunity.