The first 5,000 doses at a hospital each in Memphis and Indianapolis were administered to health care workers and first responders.
Officials acknowledge that it will be months before there are enough doses to cover significant segments of the population - distribution is difficult for many reasons. "Is it fast enough? No. But it's what's feasible and it's what can be done," says Dr Jay Butler.
Also, there aren't enough trained people to deliver the vaccines. "The workforce in both health care and public health is extremely stretched. We have let go many workers in both areas," explains Dr Michael Osterholm of the University of Minnesota
But while many people who want the vaccine will not get it for months, surveys reveal there are several others who are suspicious of the vaccine and do not want it. Medical authorities say the fears are unwarranted.
Meanwhile, the latest figures show that about a thousand people are hospitalised in the US every week for swine flu.