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  • {♫Intro♫}

  • Last week, the World Health Organization announced that the fatality rate of COVID-19 is higher

  • than we thought.

  • On March 3, they noted that, worldwide, about 3.4% of the people who had contracted the

  • infection had died from it, instead of the 2% figure that had been making the rounds.

  • There have been all kinds of reactions to that, but no matter how you feel, the key

  • thing to understand is that this number is fluid and squishy, not some unchanging property

  • of the virus.

  • Right now, we don't know how deadly this outbreak will be globally, because predicting

  • epidemics is really hard.

  • But what we all do right now can have a big impact on that final toll.

  • You might think pinning down how dangerous a disease isor what epidemiologists would

  • call its virulencewould be pretty straightforward.

  • After all, some statistics that get at this, like Case Fatality Rate or Ratio, are deceptively

  • simple.

  • You just take the number of deaths, divide by the number of cases, and boom,

  • you have the CFRand can go about comparing it to other outbreaks.

  • For example, you might have seen people saying that, on average, the seasonal flu's CFR

  • is only about 0.1%, which makes the new coronavirus 34 times as dangerous.

  • But that comparison is misleading, as the flu's fatality rate can vary between seasons,

  • and COVID-19's is likely to change.

  • See, a virus's deadliness varies based on the unique circumstances of an outbreak, and

  • we've been very wrong in the past when we tried to predict the CFR too early.

  • On the one hand, that 3.4 number could be an underestimate, because COVID-19 isn't

  • instantly fatal.

  • People who have died so far have done so two to eight weeks after their first symptoms.

  • So, some of the people currently counted as survivors may not end up that way.

  • On the other hand, it might be an overestimate because most areas are only testing people

  • who are clearly symptomatic.

  • So, the CFR might not be taking into account a large number of symptom-less and mild cases.

  • Because of these and other sources of error, experts say it can take months before you

  • can accurately predict the eventual CFR for a particular outbreak.

  • So, it may be too soon to tell where COVID-19 will fall.

  • Like, right now, experts disagree about how many milder cases are being overlooked.

  • Some think there aren't a whole lot, while others think there are tonsenough that

  • the actual CFR is already below 1%.

  • That seems to be the case in South Korea, for example, where health officials had diligently

  • tested 196 thousand people as of March 9.

  • Their CFR is hovering around 0.7%.

  • That might go up a bit if people who are very sick right now don't pull through, but it

  • may not ever hit that global average of 3.4%.

  • Which brings us to another reason CFRs can be a bit misleading: They can vary a lot geographically.

  • For example, within China, the CFR of COVID-19 has varied from about 4% to less than 1%.

  • Part of the reason for that is that things outside of the disease itselflike public

  • health infrastructure, resources, and policiescan have an impact on fatality rates.

  • That's because deaths tend to creep upward when health systems become overburdened.

  • If there aren't enough doctors, hospital beds, and supplies to give every person with

  • serious symptoms the best care, then people may die who would not have otherwise.

  • This is why you see a lot of people harping on about flu shots in places like the US.

  • The two diseases have similar symptoms, so treating flu cases can drain the resources

  • needed for treating COVID-19.

  • And non-disease factors are why it could be really helpful to slow the spread of COVID-19,

  • even if we can't stop it.

  • This is what everyone on Twitter is referring to with the hashtagflatten the curve.”

  • The idea being that, overall, the same number of people might get infected with the virus,

  • but if the cases trickle in, they're less likely to drown facilities.

  • And that means more people may survive.

  • So just by washing your hands a lot and staying home if you're sick, you can help free up

  • resources so health care workers can focus on patients with COVID-19.

  • I mean, that's not the only reason to do those things.

  • You'll also reduce the odds that you'll get the viruswhich might be worse for

  • you personally than the CFR suggests.

  • Or, better.

  • See, CFRs can help public health professionals figure out how to best respond to an emerging

  • disease.

  • But they don't do a great job of conveying your individual risk.

  • 4 Let's compare COVID-19 to the seasonal flu

  • again, because, well, everyone seems to want to do that.

  • Even if both diseases had the same CFR, they might not pose equal risks to you.

  • Influenza tends to hit both ends of the age spectrum pretty hard.

  • But COVID-19 has kind of ignored younger folks so far.

  • No one under the age of 10 died in the first 100,000 cases.

  • Meanwhile this year's flu has killed 125 kids and been especially bad for children

  • in general.

  • We don't fully understand why these diseases have such different effects on young humans.

  • But, it may have something to do with how developing immune systems react to different

  • kinds of viruses.

  • Researchers have found that the immune systems of older mice react much more strongly to

  • coronaviruses than those of younger mice.

  • Something similar could happen in humans.

  • And an immune response that's too strong can predispose people to the deadlier symptoms

  • of respiratory infections.

  • Aside from age, things like other health conditions and past infections might influence how you

  • react to being infected by this new coronavirus.

  • You can't get any of that from the overall case fatality rate.

  • Plus, you don't have to die for a disease to wreak havoc on your life.

  • In fact, some research is trying to quantify the severity of an outbreak by measuring other

  • things, like the hospitalization rate, instead of just fatalities.

  • No matter what, even if your individual risk of a severe coronavirus infection is low,

  • we should all take this epidemic seriously, because what we do right now matters.

  • We have the chance to shape how this plays out.

  • And if we do all those things you keep hearing aboutlike getting a flu shot, staying home

  • when sick, and washing our hands well and oftenwe can keep this thing from becoming

  • the worst case scenario.

  • Thanks for watching this episode of SciShow!

  • And a special thanks to our patrons, who make it possible for us to create videos like these.

  • It takes a lot of people to put together a SciShow episode and we couldn't do it without

  • our incredible community of supporters.

  • If you'd like to help us keep SciShow going, head over to patreon.com/SciShow.

  • {♫Outro♫}

{♫Intro♫}

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