The Centers for Disease Control and Prevention on Monday broadened its recommendation for COVID-19 booster shots for all adults as the new omicron variant is identified in more countries.

The agency had previously approved boosters for all adults, but only recommended them for those 50 years and older or if they live in a long-term care setting.

CDC Director, Dr. Rochelle Walensky said the new guidance reflects the emergence of the omicron variant, which has not yet been identified in the U.S. but that officials say will inevitably reach the country.

“Everyone ages 18 and older should get a booster shot either when they are 6 months after their initial Pfizer or Moderna series or 2 months after their initial J&J vaccine,” she said in a statement.

Walensky also encouraged Americans feeling unwell to seek out a COVID-19 test, saying “Increased testing will help us identify Omicron quickly.”

The World Health Organization warned Monday that the global risk from the omicron variant is “very high” based on the early evidence, saying the mutated coronavirus could lead to surges with “severe consequences.”

The assessment from the U.N. health agency, contained in a technical paper issued to member states, amounted to WHO’s strongest, most explicit warning yet about the new version that was first identified days ago by researchers in South Africa.