Coronavirus’s True Lethal Power Still Eludes Disease Experts

(Bloomberg) -- Even the world’s top infectious-disease specialists still aren’t sure how lethal a threat the coronavirus presents.

World Health Organization Director-General Tedros Adhanom Ghebreyesus said this week that the new virus has killed about 3.4% of those diagnosed, a chilling mortality upgrade that far eclipses seasonal flu’s death toll.

Tedros’s ballpark figure reflects a simple calculation, based on the number of deaths and confirmed cases. Pinpointing a reliable mortality rate may be tougher, especially since many patients may be flying below the radar, which could dramatically lower the real toll of the disease. A lot is riding on health officials’ best guesses -- including their strategy for responding to the spread.

The 3.4% mortality figure “is certainly an overestimate,” Tom Frieden, a former director of the U.S. Centers for Disease Control and Prevention and New York City health commissioner, said by email.

The WHO said the mortality rate is a “snapshot” that will inevitably change as the outbreak evolves.

Frieden said he expects that the global fatality rate for the disease, called Covid-19, will end up below 1%. In the U.K., the death rate may also be lower than that threshold, the government’s chief medical adviser, Chris Whitty, told a parliamentary committee Thursday.

Even that would be higher than the death rate from the flu, which was about 0.1% in recent outbreaks, according to CDC data. Though it would be well below the roughly 10% toll for the earlier SARS outbreak, the new coronavirus could still cause a huge number of deaths if it eventually spreads to millions of people worldwide, as some experts say it could.

Mild Symptoms

About 80% of people who get coronavirus have only mild symptoms, according to the WHO. Some experience none at all, and different testing regimes across the world cloud the picture further. If many cases go unrecognized, it allows the virus to stealthily gain a foothold in communities as well as evade tallying in the WHO ledger that experts use for analysis.

“A lot of people are asymptomatic,” said Rosanna Peeling, director of the International Diagnostics Center at the London School of Hygiene and Tropical Medicine. “We’re only seeing the cases that are confirmed and the cases of people presenting to the hospital because they can’t breathe.”

Some countries have opted to check aggressively. South Korea has conducted 140,000 tests in a short time that have uncovered about 5,700 infections. Singapore is swabbing all visitors who enter the island nation with symptoms of respiratory illness.

Virus Testing Blitz Appears to Keep Korea Death Rate Low

Japan, meantime, had tested fewer than 3,000 people as of March 3, finding 317 infections. In the U.S., health officials are trying to speed diagnosis after struggling with a number of early glitches.

Most countries follow WHO guidelines, which limit the scope of tests by establishing criteria for suspected cases. They call for checking patients who’ve had symptoms and traveled to countries where the new virus has taken hold, like China, Iran or Italy, or who came into contact with a confirmed case. They’re also testing those admitted to a hospital with severe pneumonia.

Italy’s Method

When Italy strayed from the agency’s testing recommendations, its case load swelled, rising to more than 3,000 as of Thursday -- the most outside Asia. Health authorities there counted hundreds of people who had the virus with hardly any symptoms.

Other nations simply don’t have the capacity to test widely. In Switzerland, health officials said they’ll run out of tests if the current rate continues.

Those that test the most show lower mortality rates from the coronavirus. So while the global rate may be above 3% of some 96,000 cases, it’s below 1% in South Korea. Whether that’s due to a more effective policy response, better medical care or more favorable mathematics remains unclear.

For a more structured view of the new coronavirus’s lethality, some scientists are pointing to the Diamond Princess cruise liner in Japan, where all passengers and staff were quarantined and closely followed. More than 707 people on the ship have caught the virus, with six deaths, or about 0.8%.

Serological Testing

Peeling, of the London School of Hygiene and Tropical Medicine, said a different kind of tool will soon provide additional insights into the new disease. Called serological testing, it uncovers antibodies produced by people who were exposed to the virus in the prior months.

“The only way to be sure is by looking for Covid-19 antibodies in large numbers of people, and several countries are now doing those studies,” the WHO’s Tedros said at a briefing earlier this week. “This will give us further insight into the extent of infection in populations over time.”

Unfortunately, the information provided will be a look in the rear-view mirror -- giving scientists crucial insights, but possibly too late to restrain the outbreak.

--With assistance from Todd White, Isabel Reynolds, Philip J. Heijmans, Thomas Mulier and Alessandro Speciale.

To contact the reporters on this story: Marthe Fourcade in Paris at mfourcade@bloomberg.net;John Lauerman in London at jlauerman@bloomberg.net

To contact the editor responsible for this story: Eric Pfanner at epfanner1@bloomberg.net

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