As Harvard’s Michael Mina explains toward the end of this interview, each additional variant, from Alpha to Delta to the looming Lambda, is slightly different, with a different mode of attack. Once you have a base level of immunity, exposure to these different variants helps broaden that immunity, making it less and less likely that future variants — which will inevitably continue to evolve, but have only a limited toolkit to work with in so doing — can break through in a way that leads to more serious disease. There’s risk to each exposure, in other words, but there’s also risk to avoiding exposure — the risk that you’re effectively making yourself more vulnerable to the next variant. If COVID is going to become endemic, in other words, we’re going to need to learn to live with being exposed to it — and the quicker we get used to that idea, the quicker the virus will settle down to its evolutionary end-point.

If that sounds a bit like the philosophy behind Sweden’s initial response to COVID, that’s because it is. But while Sweden’s response has been rightly criticized relative to its Nordic neighbors, which fared significantly better in the first wave of the pandemic, changing conditions can justify a change in philosophy.