A Tale of Two States

Over the past month Massachusetts had a test-positive percentage of 0.5%. That’s an increase from the prior month, but it’s still the lowest test-positive percentage in the country, tied with New Hampshire and Maine. The state has also amped up its testing a lot — second only to North Dakota of all places. Increasingly, dx tests in MA are being administered as population surveys — at universities, for example — where the intent is to identify and squelch local outbreaks before they begin. The Massachusetts covid death rate is about average and down slightly from the prior month, in step with the surprising slow downward trend nationwide. However, using death as a lagging indicator of infection, only about a third of those who get covid-infected in MA are being identified by dx testing. So the widespread MA testing protocols are missing people where the virus is already prevalent and contagion is ongoing.

Wisconsin has seen a big jump in test-positives over the past month; WI also had one of the highest test-positive percentages at 17.4%. Unlike MA, WI doesn’t do widespread testing. Also unlike MA, WI’s testing identifies pretty much everyone who’s infected, to the point of conducting and recording repeated tests on those who’ve already tested positive. It would seem that Wisconsin’s dx tests are reserved mostly for people who are experiencing symptoms and/or who have been in contact with infected people. The covid death rate in WI is still below average, and below MA, but will likely rise this month.

In short, it’s hard to compare states’ covid rates when there’s so little standardization in testing standards. That’s where a well-run CDC would help, along with a President who reinforces the recommendations.

Overall, continuity continues to prevail nationwide: the states with the highest covid death rates are still the usual Southern suspects: Arkansas, Florida, Georgia, Louisiana, Mississippi, South Carolina, Tennessee, Texas. This month they’ve been joined by North Dakota.

Which Countries are Closest to Herd Immunity?

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.