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  • Measles is one of the most contagious diseases we know.

  • Just one person is likely to infect between 12 and 18 people.

  • That number is called a disease's "basic reproduction number," or R-naught.

  • Scientists use it to describe how contagious a disease is.

  • Zika?

  • It has an R-naught of up to 6.6.

  • Super contagious.

  • But the seasonal flu?

  • Just a little over one.

  • And Covid-19, the disease caused by the [2019 novel] coronavirus?

  • Just about two.

  • That difference, between the flu and COVID-19, doesn't seem so big.

  • Especially when you look at them next to these really contagious diseases.

  • Plus, a lot of the symptoms of the flu and COVID-19 are really similar: a fever, cough, they can even both lead to pneumonia, which is ultimately how they can both be fatal.

  • So, thinking of COVID-19 and the flu as similar is a common, and frankly, understandable comparison to want to make.

  • "This is like the flu."

  • "It's a lot like the flu."

  • "I'd like to believe that it's going to end up more like the flu virus."

  • But wait, let's go back to those R-naught numbers again.

  • If the flu has an R-naught of 1.3, that means each person gets either one or two people sick.

  • After ten rounds, that's 56 total people.

  • And if we run the model with COVID-19's R-naught at two, if one person with it gets two people sick, who get two people sick

  • After ten rounds, that's more than 2,000 people.

  • This does not happen with the flu.

  • Because COVID-19 is very different and understanding "How?" is crucial to understanding how dangerous it really is and why we have to take it so seriously.

  • When we start to like, look for that comparison to the flu, we almost like, calm ourselves down.

  • But unfortunately, that's not quite the right reaction here.

  • Every year, the seasonal flu kills as many as 60,000 Americans.

  • As of late March, COVID-19 has killed about 34,000—across the whole world.

  • But scientists expect that number to go up, way up.

  • Tens of thousands of people a year die of the flubut we haven't had this for a year yet.

  • We've only had this for a few months.

  • The trouble is coming, and we can predict it, and we can see what's coming, at least to a certain extent.

  • The first really big difference between COVID-19 and the flu is how long it takes you to feel sick.

  • From the moment you're infected with COVID-19, it usually takes five days before you start to feel symptoms.

  • But it can take as long as 12 or even 14 days.

  • This is the incubation period: the time between when you catch it, and when you first realize you're sick.

  • And scientists think you could be contagious during most of this period.

  • The flu, by comparison, has an average incubation period of just two days.

  • You get sick, and pretty soon you feel sick, and you know you're contagious.

  • This is what we're used to.

  • But COVID-19 flips that around.

  • You can be contagious and spreading it around for several days, and up to two weeks, before it even occurs to you that you're sick.

  • And that leads to the next big difference.

  • No human immune system had seen this virus before.

  • Nobody has a natural immunity to it.

  • In flu season, there's always a number of people in the population who are already immune to the flu.

  • That can be because they got their flu shot, or maybe because they've already had that flu strain.

  • And that limits the spread of the virus.

  • When one person is contagious with the flu, they can only spread it to people who aren't immune who can only spread it to other people who aren't immune.

  • That's why scientists and doctors urge us to get our flu shot every year.

  • If enough people have immunity, they can kind of shield the virus from reaching others.

  • The more immunized people, the more they can protect those that are susceptible to the virus.

  • But COVID-19 is brand new.

  • None of us have had it before, and there's no vaccine, which means nearly everyone on the planet is susceptible.

  • So when a contagious person, who may not even know they're infected, comes into contact with others, it can spread like wildfire.

  • And then you see how much more dangerous COVID-19 can be.

  • Only 2 percent of people with the flu need to be hospitalized.

  • But 20 to even 30 percent of people who test positive for COVID-19 do.

  • And we're still learning about COVID-19's fatality rate, but scientists think it's somewhere between 1 and 3 percent.

  • But the flu's rate is even lower: 0.1 percent.

  • And that's a disease that can kill 60,000 people a year in the U.S. alone.

  • That's what Dr. Anthony Fauci, the US's leading infectious disease expert, tried to clear up to Congress.

  • "People always say, well, the flu does this, the flu does that. The flu has a mortality of 0.1 percent. This has a mortality of ten times that. This is a really serious problem that we have to take seriously."

  • And he's just talking about the average across all age groups.

  • For older people, or people with compromised immune systems, it can be way higher.

  • And that's especially scary when you remember all the other things that are different about COVID-19: the infectiousness, how hard it is to know that you have it, how susceptible we all are to it.

  • Estimates vary, but some scientists have warned that between 20 and 60 percent of the world's population could become infected with the virus.

  • Because COVID-19 has no cure and no vaccine, the only defense we have against it is social.

  • We can take ourselves out of the chainnot with immunity, but with social distancing.

  • Just physically not being around anyone, and staying home as much as possible.

  • But that only works if each of us takes it seriously, which is why comparing it to the flu, while understandable, is not helpful.

  • It's natural to want to find a comparison, to want to make this seem small.

  • When we use the flu as the backdrop, it almost numbs us, or it can numb us, and make us maybe even feel better about the current situation.

  • Because the current situation is bad so now is not the time to be numb.

  • We need to be vigilant, and then use our vigilance for useful actions.

Measles is one of the most contagious diseases we know.

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