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Why Covid-19 is so much worse than the flu

By Brian Resnick

Early on in the coronavirus pandemic, the question on many people’s minds was: “Isn’t this disease like the flu?” Covid-19 is a respiratory disease with some symptoms that resemble those of the seasonal flu, like fever and cough.

New evidence in the form of blood tests conducted in New York show that Covid-19 is at least as deadly as scientists have suspected for some weeks now. This is not like the seasonal flu. It is worse.

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This is not to downplay the flu, which is an annual blight we could be even more proactive about fighting (annual flu shots are important!). The U.S. Centers for Disease Control and Prevention estimates that between 12,000 and 61,000 people die of the flu every year.

But also, keep in mind: That’s in a given year. Covid-19 hasn’t been around a year — or even half a year. Before January, this virus was not known to science, at all.

Yet the virus is already responsible for around 73,000 recorded deaths in the U.S. as of May 5; and this is almost certainly an undercount. Around 2,500 people are still dying of Covid-19 every day in the United States alone, 3,800 worldwide. By the end of 2020, models suggest that the death toll in the U.S. could top 200,000 with seven million worldwide, much higher than any flu death toll in memory.

While there is still a lot of uncertainty about the coronavirus and how it will play out, based on what we know so far, this is a threat to take extremely seriously.

Reasons why Covid-19 is worse than the flu
While the exact global death rate is not yet clear, the evidence so far shows that the disease kills a larger proportion of people than the flu (and it’s particularly lethal for people older than 80).

Much of the strategy for controlling Covid-19 is based on not overwhelming medical systems.

This can be confusing because there are two figures used to describe how deadly a virus is. There’s the case fatality rate — the rate of deaths resulting from a given number of confirmed cases. And there’s the infection fatality ratio — the rate of deaths per infection, including asymptomatic infections and mild cases.

April data from New York suggests that the infection fatality rate of Covid-19 was between 0.5 and 0.8 percent, which matches international estimates. Estimates of case fatality rates are higher and vary quite a bit country by country.

That infection fatality rate for Covid-19 is much, much higher than the flu, which has an infection fatality rate of around 0.02 to 0.05 percent, according to infectious disease epidemiologist Adam Kucharski on Twitter. This means Covid-19 may be more than 10 times more deadly than the flu.

Comparing Covid-19 deaths to flu deaths may be misleading in another way, Harvard physician Jeremy Samuel Faust writes in Scientific American. The CDC flu death figures “are estimates that the CDC produces by multiplying the number of flu death counts reported by various coefficients produced through complicated algorithms,” Faust writes. The data we have on Covid-19 deaths are of recorded deaths. It’s possible that the CDC is overestimating the mortality of the flu. So comparing the two isn’t apples to apples.

But comparing recorded flu deaths to recorded Covid-19 deaths is also telling. Faust writes:

“If we compare, for instance, the number of people who died in the United States from Covid-19 in the second full week of April to the number of people who died from influenza during the worst week of the past seven flu seasons (as reported to the CDC), we find that the novel coronavirus killed between 9.5 and 44 times more people than seasonal flu. In other words, the coronavirus is not anything like the flu: It is much, much worse.”

The death rate isn’t the only reason why Covid-19 is worse. It also has a higher potential to overwhelm America’s health care system and threaten people with other illnesses or underlying conditions. Currently, there is no vaccine for the virus, nor any approved therapeutics to slow the course of its toll on the human body.

Biologically, it behaves differently than the flu. It takes one to 14 days for people with Covid-19 to develop symptoms (five days is the median). For the flu, it’s around two days. That potentially gives people more time to spread the illness asymptomatically before they know they are sick.

It’s estimated that 25 percent or more of Covid-19 infections may be asymptomatic. That’s greater than for the flu; about 16 percent of flu cases are asymptomatic, a recent Center for Infectious Disease Research and Policy report notes. “Thus, while both viruses can lead to asymptomatic infections, the asymptomatic fraction appears to be somewhat higher for COVID-19 than for influenza,” the report says.

That makes this virus sneaky. The report also says there’s evidence to suggest that presymptomatic transmission (transmission before someone feels sick) is more common with Covid-19 than the flu.

Some flu seasons are worse than others — but facilities can anticipate flu cases and prepare for them. Many hospitals, as Vox’s Dylan Scott has reported, have struggled in their preparations for Covid-19.

Several months ago, the coronavirus was believed to have made the leap from animals to humans. As far as scientists know, no human immune system had seen it before November, so there was no natural immunity to it. That means Covid-19 is more contagious than the flu — about twice as contagious, perhaps more; the numbers are still being worked out.

When a flu pandemic came through in the past, “there was there was already a lot of pre existing immunity to the virus,” Sarah Cobey, a University of Chicago infectious disease modeler, says. It’s unclear if there’s any preexisting immunity for Covid-19 based on exposure to other coronavirus strains.

The threat of it causing more outbreaks that overwhelm health systems around the world is serious. It’s bad enough to roil stock markets, put people out of work, and cause a recession. It could potentially kill millions, both in the US and abroad, in the next year or two.

It’s also possible that Covid-19 will become endemic — meaning a disease that regularly attacks humans and will not go away until there’s a treatment or a vaccine.

Again: Yes, flu variants are estimated to kill tens of thousands of people a year in the US. But we still have the flu. And now we have a new burden on top of that — making everything worse.
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Credit: Vox