(Bloomberg Opinion) -- In the absence of a vaccine or a cure, the best way to stop an epidemic is usually to isolate the people who have the disease and track down everybody they might have infected — either isolating them, too, or watching them closely for symptoms. That’s how Severe Acute Respiratory Syndrome was shut down in 2003, and how Ebola’s spread was halted in 2014.
Some infectious diseases can’t be fought this way, usually because people who’ve caught them become infectious well before they have any symptoms. Influenza is like that, which is why it’s so hard to stop even when there are vaccines. A new strain of the H1N1 swine flu virus that swept the planet in 2009, and for which a vaccine wasn’t available until late in the year, may have infected a quarter of the world’s population. Luckily, it was relatively benign — more benign than standard seasonal influenza. In the U.S., an estimated 60 million people got it, and only 12,000 died, for a case-fatality rate of 0.02%.
The case-fatality rate so far for Covid-19, the new coronavirus sweeping the world, is 3.4%. That misses a lot of undiagnosed cases, so the true fatality rate is probably closer to 1%. But that’s still 50 times deadlier than the 2009 H1N1 flu, and 10 times deadlier than the seasonal flu. It’s a lot less deadly than the 2003 SARS or 2014 Ebola, but those were both brought under control.
The big question of the moment, then, is which category of disease Covid-19 falls into. Is it a controllable disease whose spread can be halted, or an uncontrollable one destined to infect a quarter (or more) of humanity, overwhelming hospitals around the world and killing tens of millions of people? It’s not entirely an either/or. Vaccines are in the works, although they will take a while, and there are ways short of vaccines to at least slow the spread of uncontrollable diseases. It is also possible that the Covid-19 outbreak can be controlled in some countries and not others.
But the controllable/uncontrollable dichotomy is a useful way of thinking about what comes next, and also explains some otherwise-puzzling things such as World Health Organization Director-General Tedros Adhanom Ghebreyesus’s refusal so far to label Covid-19 a “pandemic.” His predecessor Margaret Chan did declare H1N1 a pandemic in mid-2009, and caught flak for it afterward because the disease turned out to be so mild. But what Chan seems to have been trying to convey was that “further spread is considered inevitable,” and what Tedros is trying to convey now is that no it’s not. “This epidemic can be pushed back,” he said Thursday.
Is he right? Maybe, and the key variable seems to be testing for the disease. If there’s a lot of it, and the tests actually work, a Covid-19 outbreak can conceivably be brought under control, as seems to be happening now in both China and South Korea.
Without effective testing, the picture is much bleaker. Early estimates of the reproduction number, or R0, for Covid-19 mostly put it above 2, meaning that each infected person is likely to infect more than two others. The average R0 for seasonal influenza is just 1.3, and for the 2009 H1N1 influenza it was 1.5. So Covid-19 may be substantially more infectious than the flu.
Still, as noted at the beginning of this column, the reason influenza is so hard to control is not just its infectiousness but also the proportion of transmission that occurs before any symptoms appear. One 2004 study estimated that for pandemic influenza it’s 30% to 50%. With Covid-19 there’s some evidence that people can transmit the virus before showing any symptoms, but a lot of uncertainty about how much transmission happens that way. A study published last week in Lancet Global Health by a group of scientists from the Centre for the Mathematical Modelling of Infectious Diseases at the London School of Hygiene & Tropical Medicine created a model for likely Covid-19 outcomes if the proportion of transmission before symptoms were 30%, 15% or below 1%. The study found that an epidemic would be almost impossible to control at 30% pre-symptomatic transmission, could probably be controlled at below 1% if more than half of contacts were tracked down, and was likely to be controlled at 15% only with a pretty heroic contact tracing (that is, more than 80% of contacts tracked down).
Widespread testing changes the equation by allowing public health authorities to identify and isolate people with the disease even if they don’t have any symptoms yet. This is what’s been happening in China and South Korea, the two countries that have been doing the most testing. In China’s Hubei province, where the Covid-19 epidemic originated, it took a brute-force lockdown to get the disease under control. But Bruce Aylward, an epidemiologist and WHO official who recently led a mission to China, told Vox.com this week that in most of the country the response “was about case finding, contact tracing, and suspension of public gatherings.” That’s what’s been happening in South Korea, too, and both countries have been reporting a decline in new cases.
In the U.S., of course, the rollout of Covid-19 tests has been disappointingly slow, with many doctors and patients complaining that even likely coronavirus cases can’t get tested. In the Washington Post today, Harvard T.H. Chan School of Public Health epidemiologist William Hanage argues that because of the testing bungle it’s “now too late to keep covid-19 from becoming established in the United States.” Mass testing will come soonish, it seems, and will probably lead to a much bigger national freak-out than we’ve had so far as it becomes clear how widespread the disease is. But it will also make it possible to start the hard work of getting it back under control.
This column does not necessarily reflect the opinion of Bloomberg LP and its owners.
Justin Fox is a Bloomberg Opinion columnist covering business. He was the editorial director of Harvard Business Review and wrote for Time, Fortune and American Banker. He is the author of “The Myth of the Rational Market.”
©2020 Bloomberg L.P.
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