if you have this many hospital beds vacant, it's okay to go to these restrictions. if case numbers are "x," you can go to "y." it's going to be different depending where you live. >> jiang: one big game changer we have been talking about is the vaccine for kids under the age of five. but on friday the f.d.a. came out and said they need more data. see how three doses of the pfizer vaccine would impact a child before making any decisions. why is that? and how could that impact the timeline? >> well, the two-dose vaccine had benefit clearly. it blocked serious illness. but the three is better. you get better correlates of immunity. the three-dose data should be complete in the next several weeks and then filed. i think what the f.d.a. wanted is to have one package, do it once and get it, so parents understood that the data were meaningful, that the vaccine was safe, and that worked. that will be the three-dose shot and hopefully that happens towards the end of march, beginning of april. >> jiang: all right, dr. david agus, thank you.