The Centers for Disease Control and Prevention (CDC) on Monday strengthened its previous recommendation for booster shots, saying that everyone 18 and older "should" receive a booster dose.

Why it matters: Last month, CDC director Rochelle Walensky accepted a key advisory committee's recommendation that adults "may" get the shot. The slight, but strengthened, change in wording comes amid the emergence of the Omicron coronavirus variant.

The big picture: Public health experts later criticized the language of the original recommendation for characterizing boosters as a "luxury" for the general population and not a necessity, Axios' Tina Reed writes.

What they're saying: "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 in a statement.

• "I strongly encourage the 47 million adults who are not yet vaccinated to get vaccinated as soon as possible," she added.
• To "stop the spread of COVID-19 we need to follow the prevention strategies we know work."

Go deeper: Experts criticize CDC's language on COVID vaccine boosters