Omicron Variant Reinfects People Who Have Had the Coronavirus

Evidence from South Africa, where the Omicron variant already dominates, shows a high rate of reinfection of people who have already had the coronavirus.,

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A past coronavirus infection appears to give little immunity to the new Omicron variant rippling across the globe, South African scientists warned on Thursday, potentially tearing away one layer of defense that humanity has won slowly and at immense cost.

Just a week after its existence was revealed to the world, the heavily mutated variant, which scientists fear could be the most contagious one yet, is already by far the dominant form of the virus in South Africa and spreading fast, according to officials there. Top European disease experts said Thursday that it could be the dominant form in Europe within a few months.

By Thursday, Omicron had been detected in 25 countries on six continents, and experts say it will soon be in every populated corner on earth. That could mean that a world already battered by two years of pandemic and — until recently — harboring hopes for recovery is instead headed for another wave of cases.

Scientists have known since early in the pandemic that the immunity gained from a coronavirus infection is not total, and probably not permanent, and that some people are reinfected. Even so, with a huge number of people already infected and recovered — about 260 million worldwide that have been detected, and in reality far more, experts say — whatever protection they had looked like an important layer in the world’s defenses.

The new variant calls that into question.

Scientists in South Africa have reported a sudden, sharp rise in November in coronavirus cases among people in that country who had already been infected, in a study that has not yet been reviewed and published by a scientific journal. The authors noted that there was no such upswing when the Beta and Delta variants emerged.

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Commuters in Soweto, South Africa.Credit…Jerome Delay/Associated Press

They did not say how many of those reinfections could be attributed to Omicron, but South Africa’s National Institute for Communicable Diseases reported on Wednesday that when it conducted a genetic analysis on a sampling of coronavirus-positive test results from November, almost three-quarters were the new variant.

“Population-level evidence suggests that the Omicron variant is associated with substantial ability to evade immunity from prior infection,” the authors of the unpublished study wrote.

In an online briefing held by the World Health Organization’s regional office for Africa, South African scientists presented a blunter version of the same conclusion, simply based on the country’s raw numbers: About 40 percent of the population has had the coronavirus and about 30 percent has been at least partially vaccinated (though there is no doubt some overlap), and yet the number of new cases is soaring.

“We believe that previous infection does not provide them protection from infection due to Omicron,” said Anne von Gottberg, a microbiologist at the communicable disease institute.

South Africa has the world’s fastest-growing caseload, though the figures are small compared to those in many other countries. In the first half of November, it was averaging about 260 reported new cases a day. On Tuesday, the figure was over 4,300, the highest in months. It jumped to more than 8,600 on Wednesday, and to more than 11,500 on Thursday.

The Omicron variant has dozens of genetic mutations not seen together before in the virus, and scientists say that the number and type of changes suggest that it is much more transmissible than earlier forms, though solid proof of that is still lacking.

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A vaccination in a suburb of Johannesburg late last month.Credit…Joao Silva/The New York Times

In fact, many crucial questions about the variant remain unanswered: Does prior infection protect against serious illness, if not against infection? Do existing vaccines provide strong immunity to it? Is the illness it causes usually milder, as some early reports have suggested?

The Coronavirus Pandemic: Key Things to Know

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The Omicron variant. The latest Covid-19 variant was identified on Nov. 25 by scientists in South Africa and has since been detected in more than 20 countries, including the U.S., which reported its first case on Dec. 1. Should you be concerned? Here are answers to common questions about this variant.

Biden’s winter Covid plan. As Omicron reaches the U.S., President Biden announced a new pandemic strategy that includes hundreds of family-centered vaccination sites, booster shots for all adults, new testing requirements for international travelers and insurance reimbursement for at-home tests.

New travel restrictions and lockdowns. Germany has announced tough restrictions on unvaccinated people, barring them from many aspects of public life. Japan, Israel and Morocco have stopped all foreign travelers, and Australia delayed reopening its borders. Here’s where U.S. citizens can travel right now and what to know about travel restrictions.

Shifting views on boosters among experts. For months, many public health experts have opposed plans to roll out Covid booster shots to all adults. But as Omicron gains ground, researchers are changing their minds, and now believe that the shots may offer the best defense against the new variant.

It will take weeks for answers to start emerging, but even in their absence, many governments around the world are taking action, imposing new restrictions on travel, particularly from southern Africa, and stepping up vaccination and testing efforts. South Korea announced on Thursday that all travelers arriving in the country must quarantine for 10 days, including fully vaccinated South Koreans, who had been exempted.

On Thursday, President Biden outlined a strategy that includes new family vaccination sites, booster shots for vaccinated adults and widespread availability of at-home virus tests, free to consumers. With the second and third Omicron cases in the United States being reported, he introduced a new requirement that any international traveler to the country show a negative test result from a sample taken within a day of departure.

German leaders on Thursday agreed to exclude unvaccinated people, except those who have recently recovered from a coronavirus infection, from much of public life, barring them from bars, restaurants, most stores and other venues. And Olaf Scholz, who will become the new chancellor next week, said he will try to mandate vaccination for all adults. That would make Germany the second country in Europe to do so, after Austria.

The Greek Parliament on Thursday voted to require vaccination for people over 60.

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Many flights to South Africa were cancelled. The international arrivals terminal at the O.R. Tambo Airport in Johannesburg on Thursday.Credit…Joao Silva/The New York Times

Europe is already suffering through its biggest pandemic wave yet, driven by the Delta variant, previously the most infectious form of the virus. Fewer people are getting seriously ill and dying than a year ago, before vaccines were rolled out, but the surge has been enough to strain health care resources yet again, and has forced several countries to backpedal on their return to normal life.

Hundreds of Omicron cases have been found in Europe already, and the rapid spread has raised fears it will prolong the current wave. The early evidence suggests that Omicron “may have a substantial growth advantage over the Delta” variant, the European Center for Disease Prevention and Control reported on Thursday.

“If this is the case,” it said, “mathematical modeling indicates that the Omicron VOC is expected to cause over half of all” coronavirus infections in the European Union “within the next few months.”

Reporting was contributed by Apoorva Mandavilli, Sheryl Gay Stolberg, Christopher F. Schuetze, Jin Yu Young, Cora Engelbrecht, Monika Pronczuk, Niki Kitsantonis and Megan Specia.

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