Data from a study of vaccine effectiveness by the Mayo Clinic shows why severe disease is hard to measure accurately. In such cases, it is better to track a proxy indicator -- a canary in the coal mine -- than the indicator of interest. Vaccine effectiveness against infection is the obvious proxy indicator for effectiveness against all outcomes, which should all vary with the number of infections. Measures of effectiveness of the existing vaccines against infection show unambiguously that the protection provided by the existing vaccines is substantially lower now than it was before the delta variant took over.

A reaction along the lines of “Who cares whether the probability of breakthrough infections is increasing; we only care about preventing severe disease” amounts to saying “Who cares that the canary died; we only care about saving the lives of miners.”

There are two mathematically equivalent ways to describe the protection that a vaccine offers against such specific outcomes as severe disease:

• relative risk

• effectiveness

Specialists understand the quirks of these two measures, but the rest of us may not until someone calls attention to them. One of these quirks is that effectiveness activates a cognitive bias that misleads people about the size of any change in the protection offered by a vaccine that is in use.

In the current context, this means that statements about effectiveness will tend to minimize the significance of the fall in protection that triggered the decision to offer a third dose of the vaccines from Pfizer and Moderna.

I have a new post that is available on its own subdomain: https://adtax.paulromer.net

It offers a specific suggestion about a policy that the citizens of the US take change and protect their social and political discourse from the rapidly growing, unchecked power of the two ad-tech giants, Google and Facebook.

As reported in today’s New York Times, in response to a request by an intermediary, I made a last ditch attempt to explain the value of testing to WH advisor Scott Atlas in an email I sent on Sept. 21.

Predictably, it had no effect. He was already dead set on chasing herd immunity.