The Centers for Disease Control and Prevention's advisory committee voted 13-1 on who would receive the vaccine in groups "1b and 1c" and who would be "essential."
Phase 1b includes people over 75 and front-line essential workers, while phase 1c includes younger patients with high-risk medical conditions and other essential workers.
Those two groups would cover K-12 teachers, school staff, child care workers and critical workers in high-risk settings.
It would also include people in homeless shelters, prisons, jails, detention centers and mental development centers and staff who work in these places, according to the CDC.
The committee also defined front-line essential workers as first responders, educators, food and agriculture workers, manufacturing workers, corrections workers, U.S. postal workers, public transit workers and grocery store workers.
The front-line essential workers represent about 30 million Americans, according to the CDC.
The CDC is expected to sign off on these recommendations to make the next phase of vaccines available to Americans over 75 and front-line workers, but it will ultimately be up to states to define which front-line workers qualify.
-ABC News' Adisa Hargett-Robinson and Stephanie Ebbs contributed to this report