MARY LOUISE KELLY, HOST:
Public health officials trying to contain the new coronavirus are trying to figure out how easily it is spread. One key question is whether people who are infected but show no symptoms can infect other people. As NPR's science correspondent Richard Harris reports, that would make it harder to hold in check.
RICHARD HARRIS, BYLINE: Some diseases seem to spread only when people are showing symptoms. That was the case with two other diseases caused by coronaviruses, SARS and MERS. But Jeffrey Shaman at the Columbia University School of Public Health says the novel coronavirus is a question mark.
JEFFREY SHAMAN: If you're going to actually contain the outbreak, which is spread very quickly, the question is, are you identifying all those cases? And if you have a lot of people who are mild or asymptomatic and not seeking medical care for a respiratory illness but are still contagious, you're going to have a very difficult time.
HARRIS: Best-case scenario is the virus would be like SARS and would not spread unless a person has symptoms. But Shaman has also looked at milder coronaviruses that circulate widely and mostly cause nothing worse than a cold. And he's found many people shed those viruses even when they report no symptoms at all.
SHAMAN: It's in their oral and nasal mucosa, and it's going to leak out as they're speaking and breathing and coughing and sneezing and wiping their nose. It will come out of them. Now, whether it's a sufficient load of virus - a sufficient quantity of virus to support making somebody else infectious - we can't discern that from what we've done.
HARRIS: What's up with the novel coronavirus is hard to say. Last week, scientists in Germany reported a case in which a visitor from China without symptoms passed the disease along to a colleague in Munich. But as Science Magazine first reported, that was wrong. The woman actually did have symptoms. Dr. Anthony Fauci, a top official at the National Institutes of Health, says that error doesn't change anything in his view. He's been talking to trusted colleagues in China about this issue.
ANTHONY FAUCI: They told me, without a doubt, there is some degree of asymptomatic transmission.
HARRIS: But he says to the extent it's happening, it doesn't explain the apparently explosive spread of this disease within China.
FAUCI: Asymptomatic transmission is not a driver of an outbreak. It may occur - and most people think it doesn't occur in a widespread way. But to whatever degree it occurs, the history of respiratory-borne illnesses say that even when there is asymptomatic transmission, asymptomatic transmission is not the main driver of the outbreak.
HARRIS: Even so, Maria van Kirkhove at the World Health Organization told reporters this question is subject of intense scrutiny right now.
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MARIA VAN KIRKHOVE: We know from a lot of experience in other diseases that people that claim to be asymptomatic - actually, when you go back and interview them, they were in the early stages of actually developing symptoms, so they weren't completely asymptomatic.
HARRIS: The most important question isn't simply about asymptomatic people but about how commonly people have such mild illness that it doesn't send them to bed or to the doctor. They are clearly at risk for spreading the disease. Dr. Fauci says as he's been watching the new coronavirus emerge over the past few weeks, that's what he's been thinking.
FAUCI: It's looking more like a really bad influenza than it is a SARS-like disease.
HARRIS: That would mean the risk of serious illness is low for most healthy individuals, but if it spreads as widely as influenza does, it could still take a lot of lives.
Richard Harris, NPR News.
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