How Bad Is the Coronavirus? Lets Run the Numbers – Yahoo Finance

(Bloomberg Opinion) -- The coronavirus outbreakhas been turning a lot of us into amateur epidemiologists. Just listen to Mick Mulvaney, the former real estate developer and member of Congress from South Carolina who is now acting White House chief of staff.The flu kills people, he said last week. This is not Ebola. Its not SARS, its not MERS. Its not a death sentence,its not the same as the Ebola crisis.

All those statements aretrue. The flu does kill people: an estimated 61,099 in the U.S. in the worst recent flu season, that of 2017-2018. People who get Covid-19, the World Health Organizations shorthand for Coronavirus Disease 2019,(1) are much less likely to die than those infected with Ebola, the Severe Acute Respiratory Syndrome of 2003and the Middle East Respiratory Syndrome first reported in 2012. And no, this is not the same as the Ebola crisis.

Its not the same as the 2014 Ebola crisis in part because it appears to be a much bigger deal for the U.S. and other countries outside of West Africa.As Microsoft Corp. co-founder Bill Gates, also technically an amateur epidemiologist but by this point quite a well-informed one, put it Friday in the New England Journal of Medicine: Covid-19 has started behaving a lot like the once-in-a-century pathogen weve been worried about.

How do we reconcile these differing views of Covid-19? Well, I too am an amateur as an epidemiologist, but I find that charts and (very simple) equations help me think through things. On the theory that others might find this helpful, too, lets start with the approximate case-fatality rates for the diseases listed by Mulvaney and a few others you may have heard of.

These fatality rates can change a lot depending on time and place and access to treatment. The Covid-19 rate is obviously a moving target, so Ive included both the 3.4% worldwide mortality ratereported this weekby the World Health Organization and the1% estimate froma study released Feb. 10 by theMRC Centre for Global Infectious Disease Analysis at Imperial College London that factored in probableunreported cases. The authors of that study also said that,given the information available at the time, they were 95% confidentthe correct fatality rate was somewhere between 0.5% and 4%. Gates used the 1% estimate in his article, and when I ran it byCaroline Buckee,an actual professional epidemiologist who is a professor at Harvards T.H. Chan School of Public Health, she termed itreasonable.

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In a context that includes Ebola and MERS, the Covid-19 death rates are much closer to those of the flu, and its understandable why people find the comparison reassuring. Compare Covid-19 with just the flu, though, and it becomes clear how different they are.

The 61,099 flu-related deaths in the U.S. during the severe flu season of 2017-2018 amounted to0.14% of the estimated 44.8 million cases of influenza-like illness. There were also an estimated flu-related 808,129 hospitalizations, for a rate of 1.8%. Assume a Covid-19 outbreak of similar size in the U.S., multiply the death and hospitalization estimatesby five or 10, and you get some really scary numbers: 300,000 to 600,000 deaths, and 4 million to 8 million hospitalizations in a country that has924,107 staffed hospital beds. Multiply by 40 and, well, forget about it. Also, death rates would go higher if the hospital system is overwhelmed, as happened in the Chinese province of Hubei where Covid-19s spread began and seems to be happening in Iran now. Thats one reason thatslowing the spread is important even if it turns out the disease cant be stopped.

Could Covid-19 really spread as widely as the flu? If allowed to, sure. The standard metric for infectiousness is whats called the reproduction number, or R0. Itisusually pronounced R naught, and the zero after the R should be rendered in subscript, but its a simple enough concept. An R0 of one means each person with the disease can be expected to infect one more person. If the number dips below one, the disease will peterout. If itgets much above one, the disease can spread rapidly.

Here are R0s for the same list of diseases as above. These are rough approximations, in most cases the midpoints of quite-large ranges. But they do give a sense of relative infectiousness.

This helps explain why public health authorities want everybody to get vaccinated against the measles. Its not all that deadly a disease, but once it gets going in an unvaccinated population, everybody gets it.

Thenumbers also seem to indicate that Covid-19 isa lot more contagious than the seasonal flu. Average R0 isnt the whole story, though. Why all the worry about MERS, for example, which with an R0 below one shouldnt spread at all? Well, its extremely deadly, its R0 can rise above one in certain environments, among them hospitals, and ... you can catch it from your camel.

Then theres SARS, which is both deadlier than Covid-19 and has a similar R0. Why was it wiped out in about a year, while some experts warn that Covid-19 may be around forever? Because SARSusually didnt become contagious until several daysafter symptoms appeared. This meant that, as four British infectious disease expertswrote in 2004, actions taken during this period to isolate or quarantine ill patients can effectively interrupt transmission. They proposed adding another variable to disease-transmission models: the proportion of transmission occurring prior to symptoms. For SARS, this was less than 11%, probably much less. For influenza, it is between 30% and 50%, making it far harder to control the diseases spread.

With Covid-19, it seems that it can transmit quite a bit before symptoms occur, Buckee says. How much is still up in the air.World Health Organization Director-General Tedros Adhanom Ghebreyesus has been arguing this week that pre-symptomatic transmission appears to be low enough that Covid-19 can be controlled in ways that the flu cannot. If this was an influenza epidemic, we would have expected to see widespread community transmission across the globe by now, he said Monday, and efforts to slow it down or contain it would not be feasible.

To understand how the spread of such a disease can be contained, ithelps to break R0 down to its constituent parts. A simple formula that I got from Buckee is:

the probability of infection given contact with an infectious person (b), multiplied by the contact rate (k), multiplied by the infectious duration (d)

In some cases you can shorten the infectious duration with treatment. Quarantining people once you know theyre infected effectively shortens it, too. Variables b and k, meanwhile, areclearly dependent on behavior. The probability of infection is reduced by things like frequent hand-washing, replacing handshakes with fist bumps and such. The contact rate is reduced by staying home. By putting much of the country on lockdown, Chinese authoritiesreduced the contact rate enough that Covid-19s R0 in the countryfell below one. They also incurred huge economic and social costs. Now,as China beginsto go back to work, the big question is whether a less-draconian approach can keep the disease in check or whether it will just start spreading again.

Thats the big question in the U.S., Europeand pretty much everywhere else on earth too. It cant be answered entirely by professional epidemiologists, either. Weighing whether the costs of a particular intervention are worth the benefits is at hearta political decision. So its actually good that politiciansare moonlighting as amateur epidemiologists. Some of them may justneed to study a little harder.

(1) The name for the virus, as opposed to the disease, is SARS-CoV-2.

To contact the author of this story: Justin Fox at justinfox@bloomberg.net

To contact the editor responsible for this story: Stacey Shick at sshick@bloomberg.net

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.

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How Bad Is the Coronavirus? Lets Run the Numbers - Yahoo Finance