we, you know, take people's word for it. we don't dig too deep. >> reporter: up to 20 million americans who got pfizer are now eligible for a booster, but health officials are urging everyone else to wait their turn. >> there will be temptations. there's an immunological reason why it's important to wait. because you know if you allow the immune response to mature over a period of a few months, you get much more of a bang out of the shot. >> reporter: this new wave of booster shots does not include moderna or johnson & johnson. an fda review of those boosters is expected in the coming weeks. but the administration today putting the focus back on the unvaccinated. >> i want to be clear, we will not boost our way out of this pandemic. >> reporter: president biden calling out the 70 million eligible americans who still haven't gotten their first shot. >> the unvaccinated overcrowd our hospitals, overrunning emergency rooms and intensive care units, leaving no room for