Biden got the vaccine before he came into office.
Trump purchased 400 million doses (200 million from Pfizer and 200 million from Moderna) in December for 2/3rd of Americans (do all Americans even want the vaccine?).
CDC reports only 38 million have been administered as of 2/14, leaving 362 million doses to be administered.
Biden purchased another 200 million doses for a total of 600 million because there was no vaccine “when [they] came into office”.