How ‘Silent Spreaders’ Make Coronavirus Hard to Beat 

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A lot of people infected with the coronavirus have very mild or even no symptoms, or ones that don’t match the usual markers of fever, dry cough or difficulty breathing. The discovery of larger numbers of so-called asymptomatic cases, initially thought to be rare, underscores a key challenge in stopping the pandemic: If people don’t know they’re infected, they’re probably not taking steps to prevent transmitting it.