Top US scientist Anthony Fauci has said that while it will take weeks to judge the severity of the new Covid-19 variant Omicron, early indications suggest it is not worse than prior strains, and possibly milder.

Speaking to AFP, President Joe Biden's chief medical adviser broke down the knowns and unknowns about Omicron into three major areas: transmissibility, how well it evades immunity from prior infection and vaccines, and severity of illness.

The new variant is “clearly highly transmissible,” very likely more so than Delta, the current dominant global strain, Fauci said.

Accumulating epidemiological data from around the world also indicates re-infections are higher with Omicron.

Dr Fauci said lab experiments that tested the potency of antibodies from current vaccines against Omicron should come in the “next few days to a week.” On the question of severity, “it almost certainly is not more severe than Delta,” he said.