The Centers for Disease Control and Prevention on Monday strengthened recommendations for the COVID-19 booster shot following the rise of the new Omicron variant.

The CDC initially said that Americans over age 50 “should” get booster shots while all other adults “may” decide to do so based on their individual risk, The New York Times reported. It is now recommending that all eligible adults should get a booster shot when they are six months after the second dose of the Pfizer-BioNTech or Moderna vaccines, or two months after the single-shot Johnson & Johnson vaccine.

“Today, CDC is strengthening its recommendation on booster doses for individuals who are 18 years and older,” CDC Director Rochelle Walensky said in a statement. “I strongly encourage the 47 million adults who are not yet vaccinated to get vaccinated as soon as possible and to vaccinate the children and teens in their families as well.”

The Omicron variant has sparked a series of new recommendations from world leaders as they navigate how to deal with the new variant that is now labeled a "variant of concern."

The World Health Organization on Monday warned that the new Omicron variant has a “very high” global risk and urged national authorities to step up pandemic relief efforts such as vaccination and testing.

“The recent emergence of the Omicron variant further emphasizes the importance of vaccination, boosters and prevention efforts needed to protect against COVID-19,” Walensky said.

Scientists do not know whether current COVID vaccines protect against the new variant but there have been no Omicron-linked deaths yet. It also remains uncertain whether this variant presents a different severity profile and whether it could escape protection against immunity induced by previous infections, the WHO said.

"To stop the spread of COVID-19 we need to follow the prevention strategies we know work," Walensky said, adding that measures include vaccination, wearing masks, improving ventilation indoors and socially distancing.