Over 42 million Americans have so far received a dose of a covid-19 vaccine, as of late January. Importantly, though, most of these people have only received the first of two doses required for the similar Pfizer/BioNTech and Moderna vaccines, currently the only vaccines authorized for use in the U.S.
Source: Gizmodo – What Could Happen If You Miss Your Second Covid-19 Vaccine Dose?