Officially, an estimated 20% of cases in China are severely ill, according to the World Health Organization. But that calculation is derived based on known cases, and would not reflect mild, undetected ones.
Without knowing for sure what percentage of cases is severe — and how easily the pathogen that causes the disease can be transmitted — it’s impossible to forecast what might happen if the virus continues to spread globally, the WHO’s emergencies chief, Mike Ryan, told reporters Wednesday.
“We don’t understand either of those parameters well enough to make accurate predictions,” he said. Still, he added a warning for people who are concluding that the virus may be less fatal than some other known pathogens: “A relatively mild virus can cause a lot of damage if a lot of people get it.”
The outbreak has infected upward of 7,700 people on the Chinese mainland, and killed 170 since the new virus, known provisionally as 2019-nCoV, was reported to the WHO on Dec. 31. Nearly 20 other countries have reported diagnosing infections in travelers from the Chinese city of Wuhan, the epicenter of the outbreak, but to date there has been little local spread of the virus in other countries.
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It’s clear there are at least some mild cases with this new infection. Many of the 100 or so exported cases are people with mild illness; to date there have been no deaths among these cases. Some of the five cases in the United States are only in hospital to ensure they don’t infect anyone else. Such cases would not be tested in China using the current case definition.
