Nationwide, the number of official Covid cases has recently been somewhat higher in heavily Democratic areas than Republican areas, according to The Times’s data. That comparison doesn’t fully answer the question, though, because Democratic areas were also conducting more tests, and the percentage of positive tests tended to be somewhat higher in Republican areas.

No single statistic offers a definitive answer. When I look at all the evidence, I emerge thinking that liberal areas probably had slightly lower Omicron infection rates than conservative areas. But it is difficult to be sure, as these state-level charts — by my colleague Ashley Wu — suggest…

The lack of a clear pattern is itself striking. Remember, not only have Democratic voters been avoiding restaurants and wearing masks; they are also much more likely to be vaccinated and boosted (and vaccines substantially reduce the chances of infection). Combined, these factors seem as if they should have caused large differences in case rates.

They have not. And that they haven’t offers some clarity about the relative effectiveness of different Covid interventions.