(CNN) While at least 12 states have identified cases of the Omicron coronavairus variant, US health officials remain concerned about the Delta version that accounts for practically all new infections.
"We now have about 86,000 cases of Covid right now in the United States being diagnosed daily, and 99.9% of them, the vast majority of them, continue to be Delta," US Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said Friday.
"And we know what we need to do against Delta, and that is get vaccinated, get boosted if you're eligible and continue all of those prevention measures including masking," she told CNN Chief Medical Correspondent Dr. Sanjay Gupta. "And those are very likely to work against the Omicron variant."
The first confirmed Omicron case in the US was identified in California on Wednesday.
Cases of the newest coronavirus variant were identified by late Friday in California, Colorado, Hawaii, Louisiana, Maryland, Minnesota, Missouri, Nebraska, New Jersey, New York, Pennsylvania and Utah, according to health officials.
Results from studies to determine the severity and transmissibility of Omicron are expected in the coming weeks.
Walensky said Omicron could become the dominant US strain but that's still unclear. The country has stepped up its sequencing work to learn more about the new variant.
"What we do know is that early data, and even mutation data, are telling us that this may well be a more transmissible variant than Delta," she added. "And so ... this is gonna take some time to sort out."
One Omicron case, in Minnesota, was in a resident who had a Covid-19 booster and health officials are trying to understand more about it, according to Walensky.
"It is helpful to understand that this person had mild symptoms that have, to my understanding, resolved pretty swiftly," she added. "So this may very well be actually a story of vaccine success, and not necessarily one of vaccine failure."
The Biden administration last week announced restrictions against travelers, with the exception of US citizens and legal permanent residents, from entering the US from eight southern African nations. The Omicron variant was first identified by South African scientists.
Pharmaceutical companies that make Covid-19 vaccines have contingency plans in place should a new vaccine be needed against the Omicron variant, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said Friday.
Data indicate that people "could probably get a good bit of mileage" from boosting with the vaccines currently in use, Fauci said during a White House Covid-19 Response Team briefing.
"Having said that, we are working with the pharmaceutical companies, particularly obviously Moderna, Pfizer and J&J, on what their plans are," he added.
"And they do have plans that have multiple contingency. One is to rev up the production of the vaccines that they already have, the next is to make, for example, a bivalent -- where you have the vaccine against both the ancestral strain and the new variant -- and the other is to make a variant-specific boost."
The US Food and Drug Administration would decide what regulatory process these vaccines would need to go through, Fauci said, "but in general, it could -- and I say could -- fall under the same situation as we do with a strain change for influenza. But I would have to leave that determination to the FDA."
Omicron carries a stretch of genetic material that looks like it may have come from a distant relative that causes the common cold, researchers said Friday.
An analysis of the many mutations that characterize the new variant shows a long stretch that looks like what's called an insertion -- a piece of genetic material that could have been taken straight from another virus or possibly even a bacteria or a human cell, according to the researchers.
Viruses are known to do this via a process called recombination.
More study is needed to know what the changes do, and it may never be known where, precisely, they came from. But they could support suggestions that Omicron is more transmissible than earlier variants, the researchers said.
The virus could have picked up the genetic material if it was infecting someone who was infected with HCoV-229E -- one of the coronaviruses that cause common colds in humans -- at the same time, the researchers said.
Viruses can also pick up stretches of genetic material from the people they are infecting. "It is plausible that the Omicron insertion could have evolved in a co-infected individual," the researchers wrote.
It's still too early to conclude whether Omicron leads to milder illnesses overall, Dr. Soumya Swaminathan, chief scientist at the World Health Organization, said on Friday.
Swaminathan, speaking at the ReutersNEXT Global Conference, noted that it has only been one week since Omicron was classified a variant of concern by WHO and a couple of weeks since it was first observed in South Africa.
"The majority of cases reported so far have reported to be mild," she said. "Many of them have been vaccinated individuals, so that could be one reason why."
She added, "But, it's too early for us to conclude that this is a mild version."