WASHINGTON, Dec. 20 (Xinhua) -- An advisory panel of the U.S. Centers for Disease Control and Prevention (CDC) voted Sunday to recommend that frontline essential workers and adults 75 years of age and older be next in line to receive COVID-19 vaccine.

The group, known as phase 1b group, is estimated to include about 49 million people, or nearly 15 percent of the U.S. population, according to the CDC's Advisory Committee on Immunization Practices.

Frontline essential workers include firefighters, police officers, teachers, corrections officers, among others, according to the committee.

These workers are in sectors essential to the functioning of society, and are at "substantially higher risk of exposure" to COVID-19, said the committee.

The recommendation came two days after the U.S. Food and Drug Administration (FDA) authorized a second COVID-19 vaccine for emergency use in the country, which is developed by American drugmaker Moderna.

The CDC advisory group voted Saturday to recommend Moderna's COVID-19 vaccine for people 18 years old and older.

Lask week, the first COVID-19 vaccine, developed by American drugmaker Pfizer in partnership with German company BioNTech, got approval from the FDA, and started to be administered to health workers on Monday.

The United States has recorded more than 17.8 million cases with over 317,400 related deaths as of Sunday afternoon, according to the real-time count kept by Johns Hopkins University.