(If first Pfizer shot can give up to 90% protection) “why do the second shot?”
Gas_Dr posted, that the literature indicates that the second shot drives TCell memory (longer term immunity).
Cathi posted a link to a Scottish study (not yet peer reviewed or published) that indicated the protection (against hospitalization for COVID), peaked four weeks after a first shot (Pfizer or AZ), and declined in weeks 5 and 6.
Perhaps a second shot really s important.
How is J and J sure to last as long as the 2 dose ones? Does it have to do with half life or whatever?