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  • episode of SciShow.

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  • {♫Intro♫}

  • This video was filmed on March 3 2020.

  • If we have a more up-to-date version of it,

  • it will be linked at the top of the description,

  • and right up there.

  • Let's go over some terminology to start.

  • SARS-CoV-2 is a virus, specifically it is

  • a new kind of Coronavirus

  • that appeared suddenly in late 2019

  • in the city of Wuhan, China.

  • Coronaviruses are common,

  • you have likely had a coronavirus lots of times,

  • it's one kind of virus that causes

  • the common cold.

  • But they can also cause SARS and MERS,

  • two diseases that have very high case mortality

  • rates.

  • They're very dangerous,

  • and the disease that SARS-CoV-2 causes

  • has been named COVID-19

  • short for coronavirus disease 2019.

  • This disease spread very quickly in China at first,

  • but new cases there are slowing,

  • and now the majority of new cases are

  • outside China.

  • This raises the question...do we have

  • a pandemic on our hands?

  • And the answer, yes, maybe,

  • also no, and also it doesn't really matter

  • and it actually

  • matters a lot.

  • So...that's why this video is here.

  • First of all, “Pandemicsounds like an official term,

  • but there aren't super hard rules

  • or numbers for when it can or should be used.

  • In general, we use the term epidemic

  • to describe a sudden, unexpected increase in cases

  • of a disease in a particular region.

  • A pandemic, on the other hand,

  • is sudden, unexpected worldwide spread

  • of a disease.

  • Why does the difference between those things matter?

  • Well, it's not just whether we get

  • to use a scarier word in the headlines

  • there's also a difference in how we respond.

  • Epidemics you contain.

  • Pandemics you can only mitigate.

  • So, then how do we decide when something

  • is a pandemic?

  • Researchers have said they'd need to see

  • evidence of sustained, domestic transmission

  • in at least one more region outside of the Pacific region that includes China, Japan,

  • and South Korea before using the termpandemic”.

  • So the question is whether these cases outside

  • the Pacific are spreading on their own.

  • Not just new arrivals, but new spread.

  • And while we didn't see any evidence of that in the early months

  • of the COVID-19 outbreak,

  • we now have seen cases that aren't directly linked

  • to either travel, or exposure to people

  • who've traveled.

  • Instead, it looks like it might be

  • what's known as community spread.

  • Community spread, or community cases,

  • are essentially when the source of the infection

  • is unknown.

  • In this case, that would mean people who

  • haven't been to China

  • and also have't been in direct contact with someone

  • who was recently in China are getting sick.

  • It's spreading from person to person

  • in their own community

  • via droplets from coughing or sneezing or just, talking loudly.

  • As of February 29th, three states in the US

  • have reported community-acquired cases:

  • California, Oregon, and Washington.

  • And a preliminary genetic analysis of the virus,

  • sampled from two separate patients in Washington state,

  • suggests that the virus was quietly spreading there for a while.

  • The virus in the two patients

  • had a particular genetic signature that only

  • a small fraction of samples from China had.

  • If the two cases were both new introductions

  • from abroad, it would be unlikely that they

  • both had that signature.

  • That suggests that there has been sustained transmission

  • in Washington state for several weeks --

  • though we'd need to find the sick people

  • who did that transmission to confirm this.

  • It seems likely that there are more cases

  • than outbreak responders are aware of,

  • probably because those people

  • simply aren't sick enough to go to the doctor.

  • So does this make this a pandemic?

  • Again, there's not a hard and fast rule,

  • but remember we'd need to see not just

  • domestic transmission, but sustained transmission.

  • So is that happening?

  • Well, many experts and scientists say yes,

  • but, as of this recording, the WHO (World Health Organization)

  • has chosen not to use the word pandemic.

  • And it so happens that the WHO

  • is having meetings between when we're filming this

  • and when you're seeing it.

  • They're the ones who get to say,

  • although even if they say it, it's not a formal term

  • -- just their assessment of things.

  • The formal use of the wordpandemic

  • was actually retired in 2009!

  • If they decide at those meetings

  • that they've seen what they're looking for,

  • they may switch from their current policy

  • of trying to contain the disease,

  • to naming it a pandemic and switching to a strategy

  • of mitigating the effects.

  • They're looking for sustained, community-acquired transmission

  • that is, many, many cases where no one knows

  • how someone got sick.

  • Now this might seem like splitting hairs,

  • but there are reasons why they might be

  • shy about making this call.

  • No one responds to news likethere's a pandemiclightly,

  • and they get that.

  • As for why we ended up in this situation in the first place,

  • we do have some ideas about why COVID-19 has been able to spread.

  • As we mentioned, it's spread from person to person

  • in droplets when a sick person coughs or sneezes.

  • It's also been suggested that a number of cases

  • are being spread by folks without any symptoms at all.

  • That's called asymptomatic transmission.

  • But on Tuesday, the WHO said that,

  • at least in China,

  • only one percent of reported cases

  • had no symptoms -

  • and most of those developed symptoms within days.

  • So it looks like asymptomatic transmission is really rare,

  • and that's unlikely to be

  • the main driver of new cases, which is very good news.

  • Pandemic or no pandemic,

  • it's important to remember that this designation

  • has nothing to do with how deadly a disease is.

  • The term only describes where the disease is spreading.

  • It doesn't tell you anything else.

  • And we're not really sure what the mortality rate of COVID-19 is.

  • It's changing so fast it's hard to even pick a number to cite.

  • For one thing, it's been different so far in China

  • than in the rest of the world,

  • and different in some parts of China than

  • in other parts of China.

  • For another, the actual rate might be much lower,

  • since mild cases may very well be going unrecognized.

  • You may have heard a figure around two percent

  • cited in the news, and that's backed up

  • by the published literature so far,

  • but it's probably not going to be the number

  • we have when the dust settles.

  • And the number's gonna be very different in places

  • with more robust healthcare systems

  • than in places that don't have lots of respirators.

  • We're planning a whole other episode for you

  • on how we understand and compare

  • fatality rates, so keep an eye out for that.

  • In the end, whether something's an epidemic

  • or pandemic may have as much to do with

  • our response to the disease as the disease itself.

  • If it's an epidemic, the nation or region where it's happening

  • may try to contain it and prevent it from getting out.

  • But with a pandemic, the focus may be

  • more on mitigation efforts,

  • like surveillance, treatment, and protecting

  • vulnerable populations.

  • They may also focus on