BRAZIL IS reeling from the coronavirus pandemic, and its agony ought to be a warning to the world. When the virus is spreading out of control and mutating as it is in Brazil, it poses a potential danger everywhere. Brazil’s surge has given rise to a new variant known as P.1 that appears to be more transmissible and may be capable of overcoming natural antibodies. So far, 10 cases in five jurisdictions have been detected in the United States, but more may be coming.

As The Post’s Terrence McCoy reports, Brazil’s death toll has reached a new high, averaging 1,208 per day over the past week, and hitting an all-time high on Tuesday. In total, 259,271 people have died. Health systems in more than half the country’s 26 states are at or near capacity. President Jair Bolsonaro has spurned efforts to combat what he calls a “little flu” and backed useless remedies such as hydroxychloroquine. The country has been consumed by internal divisions and seems unable to pull itself out from the abyss; its vaccination campaign is bogging down in shortages and delays. As with former president Donald Trump, Mr. Bolsonaro’s leadership vacuum has given the virus an opening to spread, especially from mass gatherings during the November elections, then the holidays and finally Carnival celebrations.

The most worrisome threat comes from Manaus, the largest city in the Amazon region, where the new P.1 variant apparently was spawned. It is now spreading across Brazil. Preliminary research suggests that the variant carries 17 mutations from the original coronavirus, three of them in the spike protein used to invade human cells. The new variant, like some others, is believed to be between 1.4 and 2.2 times more transmissible. But there is another aspect that is worrying researchers.

In late April 2020, a large epidemic peaked in Manaus, and the city’s hospitalizations remained stable and fairly low from May to November, despite the relaxation of control measures during that period, according to a comment published in the Lancet. A study of blood donors showed that 76 percent of the population had been infected by October 2020, higher than the theoretical 67 percent threshold for natural herd immunity.

Then, in January of this year, the virus came charging back in Manaus, leading to more deaths there in the first two months of this year than in all of 2020. What is going on? Scientists fear that the P.1 variant is reinfecting people who previously had covid-19, indicating that it can sicken those who have antibodies from the first wave. Although the conclusions are still tentative, the implications are grave: It is possible that the virus could challenge vaccines and natural immune systems.

What happens in Brazil does not stay in Brazil. As epidemiologist Miguel Nicolelis of Duke University told The Post, “If Brazil does not control the virus, it will be the largest open laboratory in the world for the virus to mutate.” That is a problem for everyone.

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