• CDC Director Rochelle Walensky said researchers are still working to understand the severity of omicron, but the public health measures used for past variants should provide some protection.
• White House chief medical advisor Dr. Anthony Fauci said omicron is now the dominant variant circulating in South Africa.
• "The almost vertical inflection of this clearly argues towards a high degree of transmissibility, Fauci said.

The omicron Covid-19 variant that has prompted global travel restrictions and fresh vaccine mandates since its discovery in southern Africa last month has now been found in 50 countries and 19 states across the U.S., CDC Director Rochelle Walensky said Tuesday.

"While 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 said during a White House Covid-19 press briefing, reiterating her call to get vaccinated.

Jeff Zients, who's leading the White House's Covid response efforts, said vaccinations have surged with roughly 12.5 million shots administered over the last week — 7 million of which were booster shots.

"That's the highest weekly total number of shots since May," he said. "So we're now vaccinating people in numbers we haven't seen since the spring."

White House chief medical advisor Dr. Anthony Fauci said scientists should have some data by the middle of next week that shows how well today's vaccines stand up to the new variant, which contains dozens of mutations that generally make it more contagious.

"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 "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.

Fauci 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.

He said 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."

There is an increased risk of people who have recovered from the beta or delta variants to get re-infected with omicron, he said. One study showed a threefold increase in the risk of re-infection with omicron over other variants, according to a slide he shared with the group. That indicates, "again without definitive proof, that there is a variation and, in fact, evasion of immunity that is induced by other variants."