Coronavirus Briefing: What Happened Today

• Concerned about Omicron, the C.D.C. strengthened its booster recommendations.

• Israel’s domestic spy agency will track Omicron patients’ phones.

• Dutch police arrested a couple who fled quarantine after one of them tested positive for the coronavirus on arrival from South Africa.

• Get the latest updates here, as well as maps and a vaccine tracker.

What we know about Omicron

We asked Dr. Anthony Fauci last week why we haven’t seen the rise of a powerful new coronavirus variant since Delta. Just a few days later, we got a possible answer.

As we told you on Friday, the new variant B.1.1.529, known as Omicron, is now raising alarms around the world. The W.H.O. warned today that global risks posed by the variant were “very high.” But there is still a lot we don’t know.

As Ashish Jha, dean of the Brown University School of Public Health, noted in a guest essay for the Times Opinion section, experts are still unsure whether Omicron is more transmissible than Delta, causes more severe disease or renders our immune defenses — from vaccines and prior infections — less effective.

Today we’re answering the most pressing questions about the variant.

How worried should I be?

Experts are urging caution, and early findings offer a mixed picture. The W.H.O. said that there was some evidence that Omicron could infect people more readily, and experts said that on paper, it may be better able to evade the body’s immune responses than prior versions of the virus.

As David Leonhardt noted in our sister newsletter The Morning, earlier variants like Delta were significantly more contagious, but the percentage of Covid-19 cases that led to hospitalization or death held fairly steady.

As my colleague Carl Zimmer wrote, “For now, there’s no evidence that Omicron causes more severe disease than previous variants.”

This afternoon, President Biden sought to reassure the nation, saying the variant was “a cause for concern, not a cause for panic.”

What’s different about this variant?

Omicron has about 50 mutations, including more than 30 in its all-important spike protein — a structure on the virus’s surface that allows it to enter the body, and that is also the part that vaccines train the immune system to recognize and attack. Having so many mutations on the spike raises concerns that Omicron might be able to invade cells or evade antibodies more effectively.

“This thing is a Frankenstein mix of all of the greatest hits,” said Dr. Stephen Hoge, the president of Moderna, referring to the variant’s many concerning mutations. “It just triggered every one of our alarm bells.”

But it’s worth keeping in mind that not all mutations play nicely together. The Beta and Mu variants, for example, had strong abilities to evade immune defenses, but they never became serious threats to the world because they were not great at spreading between infected people.

“Epidemiologists are trying to say, ‘Easy, tiger,’” said William Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health. “This could be bad. This could be very bad. But we don’t know enough to roll that tape forward.”

Will the vaccines still protect me?

Scientists said existing vaccines are likely to offer protection from the worst outcomes, including severe illness and death. However, the variant’s mutations also suggest that doses could be less effective than they were against previous variants.

The good news is that vaccine makers have said that they can tweak existing formulations to make them more effective against new variants.

A spokeswoman for Pfizer told The Times that the company’s scientists “can adapt the current vaccine within six weeks and ship initial batches within 100 days in the event of an escape variant.” Moderna said it could update its current vaccine in about two months and have clinical results in about three months if necessary.

How fast is it spreading?

It may take a few weeks to find out, but some early signs are ominous. South Africa saw a sharp increase in recent days in its test positivity rate, which rose to nearly 10 percent from 1 percent, according to data released by the National Institute for Communicable Diseases in South Africa.

That said, officials said it was still too soon to make solid assessments of whether Omicron had a higher rate of transmission, or whether it would cause more hospitalizations or severe illness.

“We simply do not have sound, reliable data on the clinical presentation,” said Salim Abdool Karim, a leading epidemiologist and H.I.V./AIDS researcher.

Where has it spread?

The variant was first detected in Botswana, where researchers sequenced the genes of coronaviruses from positive test samples; then it was quickly spotted in South Africa, Hong Kong, Israel, Australia and in a number of European countries, including the United Kingdom.

In Belgium, a young, unvaccinated woman developed flu-like symptoms 11 days after traveling to Egypt via Turkey. Officials in eastern Germany recently reported an Omicron infection in a 39-year-old man who had not traveled outside of the country, suggesting significant local transmission. The variant has yet to be detected in the U.S., although Dr. Fauci told NBC that he “would not be surprised” if it was already in the country.

How are governments responding?

Many nations have severed air links from southern Africa, where the variant was first detected. Japan, Israel and Morocco have banned all foreign visitors. In the U.S., the Biden administration restricted travel from eight nations, including South Africa, in a move that experts said would buy the U.S. time to determine how to respond.

However, some officials have said that Western countries are discriminating against southern Africa, a region that has already suffered from vaccine shortages caused by rich nations hoarding doses. South Africa has also complained that it is being penalized for its sophisticated genomic surveillance program, which allowed it to quickly warn the world of the new variant. The backlash may hinder other countries’ willingness to share data going forward.

The W.H.O. stressed the need for countries to accelerate vaccinations as rapidly as possible, particularly for vulnerable populations and for those who are unvaccinated or not fully vaccinated.

Why do we have a new variant?

Overall, the coronavirus is acquiring mutations much faster than expected. Seasonal influenza is the often cited example of a virus that mutates quickly, requiring regular updates to vaccines. But the coronavirus is “at least comparable and possibly even faster than that,” said Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.

It’s also impossible to ignore that many people in poorer countries have not yet been vaccinated, in stark contrast to people in wealthier countries. That may have given rise to conditions that were ideal for new, more contagious variants.

“Told you so,” said Francois Venter, a researcher at the University of the Witwatersrand, Johannesburg, referring to warnings from African researchers that delaying vaccinations there risked the emergence of new variants. “It feels like these rich countries have learned absolutely nothing in terms of support.”

When are we going to know more?

“Probably in a few weeks, we’ll have a better sense of how much this variant is spreading,” said Dr. Bloom, the evolutionary biologist.

Experts including Dr. Fauci have said that it could be two weeks or longer before we have more information about the variant’s transmissibility, and the severity of illness it causes.

The same goes for whether the new variant can evade vaccines. Scientists across the world — including researchers at Pfizer-BioNTech and Moderna — have rushed to test coronavirus vaccines against the new variant. But they won’t know the results for two weeks, at the earliest.

In short, it’s still early, and there is a lot we don’t know about Omicron. That said, there are reasons for hope.

Countries are responding much more rapidly to Omicron, compared with previous variants. Scientists have also figured out how to quickly identify Omicron with a standard nasal swab test known as P.C.R., which may make it easier for countries to track and manage the new variant.

There are also some positive signs coming out of South Africa, which appears to be an early Omicron hot spot. While there has been a sharp rise in hospitalizations over the past two weeks, new admissions are still relatively low, and the rate of fatalities has not increased.

What else we’re following

• President Milos Zeman of the Czech Republic, who tested positive for the coronavirus last week, appointed the country’s new prime minister while sitting inside a transparent cube.

• The Times explored the economic and human cost of barring all nonresident foreigners from entering Japan.

• A new study said movie theaters must “urgently” rethink the experience and focus on virus safety to win back customers.

What you’re doing

In Cape Town the new case rate dropped to almost zero over the last few weeks, and we were all looking forward to a carefree holiday season. Now, suddenly, we have the news of a disastrous new variant heading our way and plans are being canceled all over. So many families have not met face to face for two years or more and now must accept that they have to wait longer to see their loved ones.

— Ian Glass, Cape Town

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