Prognosis

Sweden’s Top Epidemiologist Says Herd Immunity Is a Mystery

Anders TegnellPhotographer: Anders Wiklund/AFP/Getty Images
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The man behind Sweden’s coronavirus strategy, best known for the absence of a lockdown, says key questions remain about how immunity works.

Anders Tegnell, Sweden’s state epidemiologist, says it’s still not clear to what extent transmission rates are reduced when more people have been exposed to the virus.