Screening for symptoms of COVID-19 and self-quarantine are good at preventing sick people from spreading the coronavirus. But more and more evidence is suggesting that people without symptoms are spreading the virus too.

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Monica Gandhi, an infectious diseases physician and researcher at the University of California, San Francisco, explains what is known about asymptomatic spread and why she thinks it may be a big part of what is driving the pandemic.

What does it mean to be asymptomatic?

SARS-CoV-2 – the virus that causes COVID-19 – can produce a range of clinical manifestations.