if the f.d.a. gives the green light, the boosters could begin as early as next month. healthcare workers and nursing home residents will be first in line, followed by the elderly, and then the general population. >> i think it's helpful that people can try to stick with what they started with. so if you started with pfizer, get the third immunization with pfizer, and similarly with moderna. >> reporter: the case for boosters comes after new studies, which include recent data from israel. among people 60 and older who received the pfizer vaccine, the risk of infection was 54% higher among those vaccinated in the winter, compared to the spring. >> we released those vaccines when we had to get people fully immunized in a hurry, and we did it, in terms of durability and length of protection, doing-- spacing vaccines three to four weeks apart will often not be adequate for long-term durability and hence, the need for the boost. >> reporter: hospitals continue to fill up, mostly with people who are unvaccinated.