Americans have been shockingly good at getting their second Covid-19 shot

A new CDC study delivers a different kind of good vaccine news: Americans have been incredibly diligent about getting their second Covid-19 shot.

This was a real concern about the Pfizer/BioNTech and Moderna vaccines, the first two vaccines approved for emergency use in the US, both of which have a two-dose schedule. As I wrote in December, the research literature on other multi-dose vaccines was troubling. Roughly half of patients never got their second or third dose.

One shot of these two-dose Covid-19 vaccines does confer some level of protection,...