A new CDC study delivers a different kind of good vaccine news: Americans have been incredibly diligent about getting their second Covid-19 shot. … Nearly 9 in 10 Americans, 88 percent, who were eligible to receive a second dose of either the Pfizer/BioNTech or Moderna vaccines had gotten their second shot as of mid-February. Almost all of them did so in the recommended time frame (17-25 days for Pfizer; 24-32 days for Moderna).