The paper was authored by researchers from Columbia University, Imperial College London, the University of Hong Kong, and UC Davis. What it shows is that 80% of the cases in Hubei came not from contact with those who were demonstrating what are now regarded as the “classic” symptoms of COVID-19—a dry cough, fever, and shortness of breath—but by people who either had noticed no symptoms at all, or whose symptoms were so light they never visited a doctor.
This doesn’t mean that 80% of those infected with 2019 novel coronavirus are asymptomatic, or that there were hordes of unidentified, lightly infected people out there. Studies in China, Japan, South Korea, and Singapore all seem to be in agreement that the split between light symptoms and those that range from a “bad flu” to critical is about 50/50.
What it means is that those who have light symptoms are much more effective spreaders. These results seem to mesh very well with recent statements about the ability of COVID-19 to be spread by normal talking or other face-to-face engagement.
The reason for this doesn’t appear to be magic, and it doesn’t appear to require any supercharging on the virus in people with light symptoms. It’s just that the obviously sick people were obviously sick. They tried to protect other people, and other people shied away from them. People without strong symptoms were just much more likely to engage in the kind of close contact that spreads the disease.
In fact, with 80% of cases coming from those with light symptoms, it seems clear that if the disease were only spread by those with strong symptoms, the transmission rate would likely fall below 1 and the whole epidemic would fizzle. It’s the lightly symptomatic who actually fuel the epidemic. That was true in China. It’s probably true in the U.S. It’s another reminder that if everyone acted both as if they were infected, and everyone they met was infected, the suppression created might be enough to drive the whole infection rate to nothing.
However, it’s hard to get people who feel fine to stop engaging with other people, who also feel fine. The better solution is the one that was a part of bringing the disease under control in South Korea—widespread screening and extensive testing of even those not showing symptoms until there is adequate isolation. Unfortunately, at this point no state in the country has the capacity to process sufficient tests, and especially enough high-speed tests, to carry out systematic testing of the broader population.
Instead, in state after state, we are testing only those who have symptoms—the very people who are much less likely to spread the next generation of COVID-19. Until that improves, and we can get a handle on not only those who are forced into hospital by the illness, but those who have made it through with a very mild case … act like we’re all infected.
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