Brazil coronavirus: Retreat of covid-19 in Amazon's Manaus raises questions of herd imm... - 0 views
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researchers have been studying what’s known as “heterogeneity in susceptibility.” Early herd immunity models — and vaccination campaigns — have operated from the assumption that everyone’s the same. But individuals vary: Some people are more socially active, others are more physically vulnerable.
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Heterogeneity, researchers say, reduces the percentage of infection at which herd immunity may be achieved. The people most likely to get the disease and pass it on — the most socially active, the most susceptible — catch it first. But once they’re out of the pool of potential victims, the risk is less for everyone else.
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he and other researchers estimated that population heterogeneity shaves the coronavirus herd immunity rate to 43 percent. Others say it might be lower.
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Gabriela Gomes, a mathematician at the University of Strathclyde in Glasgow, has scrutinized European cities overwhelmed by the disease. In a paper she wrote with nine other researchers, which hasn’t yet been peer-reviewed, she arrived at a striking conclusion: Herd immunity could be lower than 20 percent.
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many researchers have been reluctant to say whether they believe the worst in some of the hardest-hit cities has already passed. No one knows how long immunity lasts. The virus could mutate.
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“I would love that as well. But the reality is that it’s wishful thinking. It’s confirmation bias. We can’t pick evidence we hope is true. We have to be very careful about this because it could blow up in your face very quickly.”
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Officials weren’t willing to impose a lockdown. In impoverished Manaus, where many already live on the brink, the mayor said it would lead to social chaos and violence. So Pinheiro Alves spent his off hours trying to jury-rig ventilators.
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“There isn’t a concrete explanation,” said Henrique dos Santos Pereira, a scientist at the Federal University of Amazonas. Maybe there’s an unseen biological immunity in the population. Or the city’s relative youth staved off the worst.
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“The problem is that we don’t know how many people are susceptible,” dos Santos Pereira said. “In the beginning, we were thinking it was everywhere, but it doesn’t seem like the whole world is susceptible … It is causing us to reconsider the theory of herd immunity.”
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Virgílio, the mayor, hopes the scientists are right. The medical system in Manaus has failed once. If a second wave does come, he has little doubt what would happen.“Our capacities would be overwhelmed.”