Officials plan to ship 12.5 million doses of Moderna's vaccine following an emergency authorization, he added.
There are roughly 21 million health-care workers and 3 million long-term care facility residents in the United States, according to the CDC.
Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, said most states and local jurisdictions expect it to take three weeks to vaccinate all of their health-care workers.
Pfizer's and Moderna's vaccines require two doses about a month apart.
States have already submitted early plans to the CDC on how they intend to inoculate some 331 million Americans against Covid-19 once a vaccine is approved.