A top U.S. infectious disease expert reportedly said that the omicron COVID-19 variant is "almost certainly" not more severe than the delta variant.

Speaking to AFP on Tuesday, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said early indications suggest the omicron variant might be even milder.

Fauci, however, cautioned that much about the variant is not yet certain, saying that it will take several more weeks to fully determine the precise severity. 

The chief medical adviser for U.S. President Joe Biden said the new variant is clearly highly transmissible, very likely more so than delta, the current dominant global strain.

Regarding the severity, the expert reportedly said it almost certainly is not more severe than delta. He also said data about the effectiveness of vaccines on the variant should be available in the next few days to a week.