Even if natural immunity is relatively ephemeral, there is no point in using scarce vaccines for someone who is immune now when those doses could protect someone who has no immunity. Vaccine supplies will be more abundant if and when natural immunity wanes in six months or a year.

The CDC’s recommendation that serologic blood testing for antibodies should not be used for “vaccine decision-making” makes no sense. If a patient knows or thinks he had COVID-19 in the past, his current immune status can be confirmed with serologic testing. The FDA found that most of the serology tests for which it has granted emergency-use authorizations are highly accurate, so there is little chance the patient would be misled into declining a vaccine by a false-positive test. Following up with periodic serologic testing will show whether immunity has diminished to the point where vaccination can be recommended.

Pandemics end when the combination of natural immunity and vaccine-induced immunity covers a high-enough percentage of the population — thought to be about 70 percent for COVID-19 — to stop viral transmission.