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Why are people's responses to SARS-CoV-2 infection so variable — from asymptomatic to lethal? The age and health of the person and the size of the inoculum are obvious factors. A new study identifies aspects of the immune response that also affect the outcome.
An international team experimentally infected 16 healthy young adults with low doses of an early SARS-CoV-2 variant and followed the volunteers closely for 1 month. The participants had not been infected with, nor vaccinated against, the virus previously. Immune-system measurements involving cells from both blood and nasal swabs were made both before and after infection. Six participants had persistently positive viral tests and mild symptoms. Of the remaining 10 people, 3 had intermit…