The update comes after President Joe Biden on Monday called for wider vaccination to curb the spread of the Omicron coronavirus variant, which was first detected in southern Africa.
The US health regulators last week expanded the eligibility for booster shots of COVID-19 vaccines to all adults aged 18 and older either six months after their initial Pfizer or Moderna vaccine doses or two months after their Johnson & Johnson shot.
The CDC had, however, stopped short of saying all adults aged 18 to 49 should get the additional shots.
The agency is taking a more cautious stance as Omicron's emergence further emphasizes the importance of vaccination and boosters, CDC Director Rochelle Walensky said in a statement on Monday.
Amid the renewed emphasis, Pfizer and partner BioNTech are expected to ask the US Food and Drug Administration (FDA) in the coming days to authorise their booster shots for those aged 16 and 17 years, the Washington Post reported on Monday, citing sources.
Separately, the Wall Street Journal reported that the FDA could approve booster doses for 16 and 17 year-olds as soon as next week.
Pfizer, BioNTech and the FDA did not respond to requests for comment.
Omicron, which the World Health Organization said carried a very high risk for fueling infection surges, has now been confirmed in several countries including Germany, Hong Kong, South Africa and Canada.
Scientists in the United States and around the world are urgently examining vaccine effectiveness related to this variant, the CDC said.
The agency also said the 47 million adults who are not yet vaccinated are encouraged to get vaccinated as soon as possible.