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The Brazil coronavirus variant now found in the UK appears more contagious and may evade immunity provided by past infection, scientists say.

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Dr. Faria and his colleagues looked for coronavirus antibodies in samples from a Manaus blood bank in June and October. They determined that roughly three-quarters of the residents of Manaus had been infected.

But near the end of 2020, new cases began surging again. “There were actually far more cases than in the previous peak of cases, which had been in late April,” Dr. Faria said. “And that was very puzzling to us.”.....

Combining the data from genomes, antibodies and medical records in Manaus, the researchers concluded that P.1 conquered the city thanks not to luck but biology: Its mutations helped it spread. Like B.1.1.7, it can infect more people, on average, than other variants can. They estimate it is somewhere between 1.4 and 2.2 times more transmissible than other lineages of coronaviruses.

But it also gets an edge from mutations that let it escape antibodies from other coronaviruses. They estimate that in 100 people who were infected with non-P.1 lineages in Manaus last year, somewhere between 25 and 61 of them could have been reinfected if they were exposed to P.1 in Manaus.

The researchers found support for this conclusion in an experiment in which they mixed P.1 viruses with antibodies from Brazilians who had Covid-19 last year. They found that the effectiveness of their antibodies dropped sixfold against P.1 compared with other coronaviruses. That drop might mean that at least some people would be vulnerable to new infections from P.1.

Dr. Faria said “an increasing body of evidence” suggests that most cases in the second wave were the result of reinfections.