The U.S. Centers for Disease Control and Prevention said on Monday everyone aged 18 years and older should get a booster shot either six months after their initial Pfizer or Moderna vaccine doses or two months after their Johnson & Johnson shot, as the omicron threat looms.

The update comes after U.S. health regulators last week expanded the eligibility for booster shots of COVID-19 vaccines to all adults, but stopped short of saying all adults aged 18 to 49 should get the additional shots. "The recent emergence of the omicron variant (B.1.1.529) further emphasizes the importance of vaccination, boosters, and prevention efforts needed to protect against COVID-19," CDC Director Rochelle Walensky said in a statement on Monday.

The agency also said the 47 million adults who are not yet vaccinated are encouraged to get vaccinated as soon as possible, adding that children and teens should also be vaccinated to lower chances of a serious illness