Now that every American adult is eligible to get vaccinated, vaccine makers are shifting their priorities to meet the changing needs of people will need to be vaccinated in coming months.

On April 29, Pfizer-BioNTech announced that it will begin shipping smaller packages of its COVID-19 by the end of May. Currently, the companies’ vaccine comes in packs of 195 vials, each of which contains about six doses of vaccine, for a total of around 1,100 doses. That size is useful for the mass vaccination centers that have been the focus of the U.S. vaccination program so far, with their goal of immunizing hundreds or even thousands of people a day. But it’s actually prohibitive for smaller doctors’ offices and pharmacies, which might be able to only vaccinate a few dozen people a week, no matter how many doses they have on hand. The company’s new packs will contain three containers of 25 vials each, for a total of 450 doses. The outer shipping container, which can serve as a temporary ultra-cold freezer at temperatures of around -70°C for the vaccine as long as it is replenished with dry ice for up to 30 days, will remain the same.