only about one-quarter of vaccinated americans have gotten their booster -- you got yours. i got my booster. tell viewers why they should get them, too. >> part of this may be changing in terms of the definitions just mentioned, the idea that fully vaccinated might mean three shots. i think that would make a big difference. why should they get it? we are getting more and more data. israel has always sort of given us data a few weeks if not months in advance so if you look at the impact of boosters now, up until quite recently, coming up until the beginning of december, boosters started there at the end of august. numbers were going up. admittedly israel was already doing a pretty good job. though the numbers were going up they were still relatively small. you see what happened with boosters over the next few months after that. that's cases. if you look at deaths over all you also saw a significant impact of boosters.