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The coronavirus variant Omicron has arrived in the United States: Here’s what we know

Shoppers at a mall in Johannesburg on Friday. A new coronavirus variant first detected by scientists in South Africa has sparked jitters across a pandemic-weary world.Denis Farrell/Associated Press

The Omicron variant of the coronavirus has arrived in the United States, the US Centers for Disease Control and Prevention said Wednesday. Governments are on alert as scientists scramble to determine what the impact of the variant will be on a pandemic that has already killed more than 5.2 million people worldwide. Here, compiled from Globe wire service and major media reports, is what you need to know about the latest developments in the Omicron story:

What is a variant?

Variants are mutations of the coronavirus. Scientists say viruses constantly mutate naturally as they replicate and circulate in their hosts. Sometimes these mutants disappear. Other times they persist and can outcompete rival variants. The World Health Organization last Friday deemed the new mutation a “variant of concern,” and, using its Greek letter naming convention, called it Omicron.


Where was this new variant found?

The variant, technically known as B.1.1.529, was reported on Thanksgiving by South African health officials. Experts said it was likely already circulating through other countries — and they were right. As of Wednesday, in addition to the United States, about two dozen countries had announced that they had detected cases of Omicron.

What’s the latest on the US case?

The CDC announced Wednesday that Omicron had been detected in California. The agency said the case was detected in a traveler who had returned from South Africa on Nov. 22. The person was reported to be fully vaccinated with the Moderna vaccine but had not had a booster shot. All that person’s close contacts have been contacted and have tested negative. “CDC has been actively monitoring and preparing for this variant, and we will continue to work diligently with other U.S. and global public health and industry partners to learn more,” the agency said in a statement.


What’s different about this variant?

Scientists say Omicron has an unusual number of mutations and they are concerned that those could spell trouble, worsening a pandemic that has already wracked the world.

Omicron has a “very unusual constellation of mutations,” Tulio de Oliveira, director of South Africa’s KwaZulu-Natal Research and Innovation Sequencing Platform, said last week. “This variant did surprise us — it has a big jump in evolution, many more mutations than we expected, especially after a very severe third wave of Delta.” The Delta variant currently accounts for nearly 100 percent of cases in the US and continues to cause illness and death at a high rate.

Trevor Bedford, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle and a recent winner of a MacArthur “genius grant,” said in a virtual event held Tuesday that the number of mutations in the spike protein that allows the virus to penetrate cells is “kind of wild.”

“So other things that have been circulating — Alpha, Beta, Gamma, Delta, etc. — have maybe eight mutations, maybe 10, in the spike protein. That’s largely what’s given them their advantageous phenotype. So Omicron ... it kind of comes out of nowhere, perhaps from an immunocompromised individual, and shows up with 30 mutations in the spike protein,” Bedford said.

“It looks striking. It looks worrisome,” he said, and “already seems like it will be functionally different.”

Why do the mutations matter?

Scientists are working feverishly to determine exactly how the mutations may have changed the virus. Crucial questions remain unanswered, including whether the variant is more transmissible, whether it causes more severe disease, and what its impact is on “existing countermeasures” such as vaccines, according to a statement released Sunday by the World Health Organization.


The WHO said that it appeared Omicron might pose an increased risk of reinfecting people who had already had COVID-19, but “information is limited.”

The health agency also said widely used PCR tests were able to detect the variant, while studies were underway to see if it could be detected by rapid antigen tests like those people can purchase for home use. Some treatments still will be effective against the variant, while the effectiveness of other treatments still needs to be studied, the statement said.

The WHO warned in a separate technical brief to member countries that “the likelihood of potential further spread of Omicron at the global level is high. Depending on these characteristics, there could be future surges of COVID‐19, which could have severe consequences.” The agency assessed the overall global risk as “very high.”

Experts say it will take a couple more weeks before there is more clarity.

But a top WHO official ventured Wednesday that vaccines would continue to provide at least some level of protection against Omicron.

“We know that vaccines are likely to have some protection,” WHO chief scientist Soumya Swaminathan said in a press briefing. “We still need to find out if there’s any loss of protection, but we think vaccines will still protect against severe disease as they have against the other variants.”


How worried should we be?

While scientists have sounded alarms, others, including President Biden, have urged people to remain calm. Biden said at a news conference Monday that the variant should be “a cause for concern, not a cause for panic.”

“We should not be freaking out,’’ Dr. Anthony Fauci, the nation’s top infectious disease doctor and a top adviser to Biden, said Monday on “CBS This Morning.” “It’s not the time to panic. We should be concerned.”

The variant “has features that warrant concern, but there’s so much unknown that it’s not a reason to panic as of today,” Dr. Dan Barouch, head of the Center for Virology and Vaccine Research at Beth Israel, which helped develop the J&J vaccine, told the Globe last week.

Dr. Ashish K. Jha, dean of the Brown University School of Public Health, said on Twitter Sunday that the Omicron variant would not “set us back to square one,” saying that tests and therapies will still work while vaccines “MAY take a hit but will still provide some (may be a lot) [of] protection.”

Have we been through this before?

Yes. The warnings about the new variant are reminiscent of those raised when the Delta variant was first sighted. Eventually, the Delta variant did make its way to the US and became predominant, causing a deadly surge.

The case of another variant, Mu, provides a more hopeful example. People were worried about the Mu variant in September, but it never turned into a major threat.


What impact has the news about the variant had?

Dozens of countries, including the United States, have imposed a variety of travel restrictions, hoping to slow, if not block, the arrival of Omicron.

The actions began within hours of the announcement on Thanksgiving by South African officials. In the past, it’s taken days, weeks, or months for such restrictions to be imposed.

Uncertainty about Omicron has also roiled the world’s financial markets in the past few days. The CDC on Monday also strengthened its recommendations on booster shots, encouraging all adults to get them.

What can people do now?

Experts and officials are calling for people to get vaccinated and get their booster shots if eligible, and for stepped-up efforts to vaccinate the world.

“You have to get your vaccine — you have to get the shot, you have to get the booster,” Biden said at the Monday news conference.

“We have the best vaccine in the world, the best medicines, the best scientists, and we’re learning more every single day. And we’ll fight this variant with scientific and knowledgeable actions and speed, not chaos and confusion,” he said at a White House news conference.

Fauci said Monday on CBS, “Our concern should spur us to do the things that we know work. So rather than ... freaking out and rather than panicking, just do the right thing.”

Fauci said the “right thing” includes getting vaccinated or getting a booster shot of the COVID-19 vaccines.

The WHO said in its statement, “The most effective steps individuals can take to reduce the spread of the COVID-19 virus is to keep a physical distance of at least 1 metre from others; wear a well-fitting mask; open windows to improve ventilation; avoid poorly ventilated or crowded spaces; keep hands clean; cough or sneeze into a bent elbow or tissue; and get vaccinated when it’s their turn.”

John R. Ellement, Ryan Huddle, and Jonathan Saltzman of the Globe staff contributed to this report. Material from Globe wire services was used.

Martin Finucane can be reached at