months since i got the other. what do you say to that person? >> well, we know that there are people who have already been doing that, before today. i would say there's pretty good evidence from other vaccines and probably this will be true for covid-19. that you want to leave a pretty good interval between your initial immunization and that booster. you want to give the immune system a chance to mature its potential to generate new antibodies. and that probably means going quicker than, say, six months. might actually give you less benefit than if you can hang on and wait until at least six and better yet, eight. >> interesting. nih director, dr. frances collins, really appreciate it. thank you. want to get perspective now from our chief medical correspondent, dr. sanjay gupta. and cnn medical analyst, dr. leana wen, former baltimore health commissioner. so, sanjay, what do you make of what dr. collins just said? >> well, even up until yesterday, there was a lot of back and forth on this. not a slam-dunk decision, so to speak.