4 out of 5 cases of COVID-19 in China were acquired from people with few or no symptoms

TODAY / YouTube More COVID 19 Cases Confirmed In 1582660309.jpg...
TODAY / YouTube

The rise, substantial containment, and flattening of the COVID-19 outbreak in the Hubei Province of China has become the model that much of the world would like to imitate—in results, at least. Though many people suspect—for very good reasons—that China could be lying about the death rate in Hubei, there seems little doubt that when it comes to the overall course of the epidemic there, the Chinese government managed to wrangle the disease into something that looks very like stasis. On Tuesday, China indicated only 1,240 active cases remaining in that country, with 240 in hospitals, and 1,000 in very, very tight observation.

The actions that were taken in Hubei were often extreme, which makes the curve generated there a questionable model on which to base the potential arc of the epidemic in the United States. However, the outbreak in and around the city of Wuhan has become the best-studied incident of this disease, and an invaluable source from which to draw insight when it comes to COVID-19. That includes a paper that was published by researchers from multiple universities showing that when it came to the source of cases, those with the mildest symptoms were the most likely to pass it along.

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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