Dr. Anthony Fauci, the US top expert on infectious diseases, told CNN in an interview on Sunday that early indications of the severity of the Omicron COVID-19 variant are "a bit encouraging," though he stressed that more information was still needed.

"Omicron has a transmission advantage" in South Africa, where the variant was first reported, Fauci said, adding the country had a low level of cases before it saw "almost a vertical spike upwards, which is almost exclusively Omicron."

"Though it's too early to really make any definitive statements about it, thus far, it does not look like there's a great degree of severity to it," he noted, adding, "Thus far, the signals are a bit encouraging."

Fauci also commented on the travel ban imposed by the US on South Africa and seven other southern African countries in the wake of the discovery of the Omicron variant.

“As we're getting more and more information about cases in our own country and worldwide we're looking at that very carefully on a daily basis. Hopefully we'll be able to lift that ban within a quite reasonable period of time,” he said.

Fauci added the administration is reevaluating the policy “in real time, literally, on a daily basis.” He explained that the travel restrictions were imposed at a time when the US was "really in the dark" and "had no idea what was going on except that there seemed to have been an explosion of cases of omicron in South Africa."

The ban was implemented “to give us time to figure out just what was going on.”

US President Joe Biden said last week that the newly discovered Omicron variant “is a cause for concern, not a cause for panic.”

“We have the best vaccine in the world, the best medicines, the best scientists, and we're learning more every single day. And we'll fight this variant with scientific and knowledgeable actions and speed, not chaos and confusion. We have more tools today to fight the variant than we've ever had before,” he added.

Later, the US Centers for Disease Control and Prevention (CDC) issued a new guidance recommending booster shots for all vaccinated people 18 and older.

The guidance, which previously said adults “may” get boosters, now says they “should” get a third dose of the Moderna or Pfizer shot six months after their second dose. The same recommendation applies to those who received the single-shot Johnson & Johnson vaccine but after only two months.