The Omicron Covid-19 variant, discovered two weeks ago in southern Africa, is now present in 50 countries, the US CDC Director Rochelle Walensky has said.
The super mutant strain of Covid is also present in about 19 states in the US, Walensky said during a White House Covid-19 press briefing on Tuesday.
She said the US is currently "seeing about 100,000 new cases of Covid-19 each day".
"While much of the news is focused on the new Omicron variant ...I want to reiterate that over 99 per cent of sequenced cases in the United States continue to be from the Delta variant," Walensky said.
However, "we are still working to understand the severity of Omicron as well as how it responds to therapeutics and vaccines, we anticipate that all of the same measures will at least, in part, provide some protection against Omicron," Walensky noted.
According to White House chief medical advisor Dr. Anthony Fauci, scientists will have some data by the middle of next week that shows how well current vaccines stand up against the new variant.
On Omicron's transmissibility, Fauci said: "We have molecular evidence to suggest that the mutations that are seen in Omicron and in other variants would suggest that they are associated with increased infectivity."
He also pointed to "real-world evidence" that "determines increase in cases, possible increase in reproductive number, and the rapid replacement of Delta by Omicron in certain situations."
He said "real-world evidence" in epidemiology and clinical studies will definitively answer how transmissible and severe the virus is as well as whether or not it can evade vaccines.
The US infectious disease expert also pointed to a chart that showed a seven-day rolling average of confirmed Omicron cases per 1 million people in South Africa, noting that it is now the dominant variant circulating in the country. "The almost vertical inflection of this clearly argues towards a high degree of transmissibility," he said.
However, Fauci noted it was too early to determine the severity of the disease. While data released over the weekend from South Africa indicates Omicron might cause more mild illness, he cautioned, "however, this can be influenced by the fact that many in this particular cohort are young individuals."
"We'll be able to determine whether or not antibodies induced by all vaccines lose their capability of effectiveness with Omicron," Fauci said of studies looking at both live virus and "pseudo virus."
"In addition, we are doing animal studies to evaluate immune protection as well as efficacy of antivirals," he said.
Further, he stated that there is an increased risk of people who have recovered from the Beta or Delta variants to get re-infected with Omicron. A recent South African study showed a three-fold increase in the risk of re-infection with Omicron over other variants. This indicates, "again without definitive proof, that there is a variation and, in fact, evasion of immunity that is induced by other variants," Fauci said.