authorization for the vaccine for children, and it's about finding the level of efficacy amid a ongoing trial involving a third dose of the vaccine. >> given the fact that that is changing, that's evolving, new data is accruing. it's hard for the fda to give its advisers a fixed snap shop what of efficacy, so if they wait longer and administer the third dose in that clinical trial, they will have a better measure of the effectiveness, but they will have a very firm picture of what level of effectiveness the vaccine is delivering. >> across the united states, hundreds of thousands of vaccine doses are being administered daily, but so far cdc data shows less than 30% of the u.s. population has received the third shot, the booster shot. meantime hong kong is reporting more than 1,300 new covid