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Health authorities have identified a new variant of the coronavirus with some alarming characteristics. It first cropped up in Botswana and is believed to have contributed to a sharp rise in infections in South Africa. On Friday, the World Health Organization officially named it a “variant of concern,” meaning there’s evidence that it’s more transmissible or more virulent than previous versions of the virus.

Scientists are particularly worried about this one, known as omicron, because it has an unusual number of mutations — more than have been found in other highly transmissible variants such as delta. Many appear on the spike protein, the part of the virus that binds to human cells and enables it to gain entry. The fear is that these changes could help omicron more easily get around the body’s immune defenses and render the vaccines less effective. “This is the most concerning variant we’ve seen since Delta,” Eric Topol, director of the Scripps Research Translational Institute, told The Washington Post.

The announcement of the new variant sent financial markets tumbling, prompted countries around the world to restrict travel from southern Africa, and set off a frantic scientific effort to figure out just how dangerous the evolved pathogen might be. Such a reaction is to be expected at a time when delta is already resurging across Europe and the United States. But it’s important to keep the situation in perspective. Scientists still know little about the new variant outside its mutation profile. And so far only a few dozen confirmed cases have been identified in a handful of countries. Public health recommendations haven’t changed: get vaccinated, get boosted, get tested when you’ve got symptoms, and mask up in risky settings. Read our FAQ on the variant for more.

As the Biden administration tries to gauge the threat from omicron, the United States will restrict travel from South Africa and seven other countries in the region. A senior administration official tells my colleague Annie Linskey that the policy is being implemented in “an abundance of caution in light of a new covid-19 variant circulating in Southern Africa.” The decision came after the White House arranged a meeting between U.S. and South African doctors to learn more about the variant’s spread. “We want to find out scientist-to-scientist exactly what is going on,” President Biden’s chief medical adviser Anthony S. Fauci said in a CNN interview.

As shoppers hit the stores for Black Friday, the Dow plunged more than 900 points on news of the new variant, marking its worst day of 2021. Airline and cruise company stocks dropped. So did oil prices. But investors flocked back to companies that did well during the first year of the pandemic, including Zoom and Peloton.

Infections continue to soar in Michigan, now the country’s virus epicenter. Covid-19 patients, most of them unvaccinated, are flooding into hospitals across the Wolverine State, pushing the health-care system into crisis. The state’s caseload has hit a record high, and hospitalizations are soon expected to do the same. One health executive described the situation as “almost unmanageable.” At least two dozen other states have seen cases rise at least 5 percent in the past two weeks, signaling that the fifth pandemic wave predicted by health experts is indeed upon us.

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