The simplest explanation for the Delta surge is still the best one

As the Delta variant continues to sweep through countries around the world, including countries like Australia that were once poster children for a zero-COVID strategy, it’s understandable that anxiety is on the rise. Is vaccine effectiveness waning so fast that we’ll all need booster shots? Is Delta more dangerous to younger people? Do we all need to go back into lockdown? And the flip side to anxiety is fatalism: If vaccine effectiveness fades so fast, why bother getting the shot in the first place?

At times like these, it’s useful to take refuge in an old standby: Occam’s Razor.

Occam’s Razor is frequently described as a preference for the simplest explanation that fits the facts, but that’s potentially confusing, as what constitutes a “simple” explanation isn’t always . . . simple. We see the sun rise in the east and set in the west; the “simplest” explanation would appear to be that the sun revolves in a circle around the Earth, along with the moon and the stars. But making this “simple” explanation work required increasingly elaborate add-ons to make it fit all the observed facts. When Copernicus came along with a heliocentric model in which the Earth was only one of several planets, it didn’t actually fit the facts better in the sense of being more accurate; that would come with Kepler’s refinement of the model from circular to elliptical orbits, and Newton’s laws that explained that motion. But it was simpler in the sense that it required substantially fewer postulates; you didn’t need a complex collection of epicycles that themselves had no explanation to explain why the planets wandered around the heavens as they did.

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