the novel coronavirus that has often made it difficult to separate fact from fiction.

And that's because with each day, we're learning more about the virus behind this global pandemic.

As new data has radically altered the scope of COVID-19, we wanted to take this chance

to cut through all the misinformation and take a closer look at what exactly it is,

the latest info about how it attacks our bodies, and how its stealthy nature has completely shut down our world.

We haven't been in a situation like this in over 100 years.

No one has experienced a virus that's had this combination of ease of transmissibility and mortality.

I'm Timothy Brewer.

I'm an infectious disease doctor and professor of medicine and epidemiology at UCLA.

I've been an infectious disease physician for about 30 years and an epidemiologist for 25.

Known for the spike proteins on their surfaces, coronaviruses are a large family of viruses

that can cause respiratory illnesses like the common cold and more severe ones like

SARS, MERS and of course, COVID-19.

And here's what we know so far about what the virus does to your body.

Once it enters the respiratory tract through the nose, mouth, or eyes, it attaches itself

to the surface of a cell likely via a receptor called ACE2.

The virus then fuses with the cell's membrane, and releases its RNA.

The infected cell then begins to make copies of the virus that will continue their invasion throughout the body.

But when it comes time for the immune system to fight back, it's a bit of a mixed bag

when it comes to the human body's response.

While the majority of cases are mild,

Severe disease occurs in about 15% of individuals, and about 5% of individuals are so sick that

they need to go into an intensive care unit and probably end up on a ventilator.

Now keep in mind, most of the statistics we have come from a study of roughly 72,000 COVID-19 patients in China.

In this study and others since, severe cases displayed an intense cough, high fever, shortness

of breath—and in some cases, pneumonia.

In the more extreme cases, there has been increasing evidence that patients' immune

systems are overreacting to the virus in a specific way.

So the cytokine storm are the chemical signals that the immune system is releasing to basically

call out all the forces to try to eliminate the virus.

And in the process of doing that, they can also damage normal cells like cells in the

lung that make it difficult or impossible for the individual to breathe.

And since our organs need oxygen to function, complications from the disease can lead to organ failure and even death.

And if you still think that these severe cases only affect the elderly or those with pre-existing

conditions—like diabetes, heart disease or asthma—think again.

Recent CDC data reported an increased number of hospitalizations among healthy adults in

the U.S. between the ages of 20 and 54 years old.

Why one person will develop very severe disease and potentially die and another person not

is not entirely clear, but it's probably genetically determined by small differences in the way

your immune system works and responds to a certain pathogen.

My name is Dr. Larry Lutwick.

I'm a professor of medicine at the Mayo Clinic, School of Medicine and Sciences.

I've been in infectious diseases for 40 some odd years.

Now for those who experience a milder form of COVID-19, diagnosis can be difficult to pin down.

Common symptoms include low-grade fever, fatigue, and a dry cough, but as we learn more about

the disease, there have been reports of a much wider and surprising array of effects.

A notable symptom that has occurred is loss of smell.

Why some people are presenting with diarrhea as the first manifestation?

Why some people, are presenting as if they're having a heart attack with severe chest pain without any cough at all?

Luckily about 80% of cases will experience this milder form of the disease.

But what makes COVID-19 so mysterious is that its milder cases can look like the common

cold or the flu or even go completely unnoticed.

What we're learning from COVID-19 is that individuals are infectious, before they

have any symptoms like fever, cough, or sore throat.

An asymptomatic case is someone who would test positive without ever developing symptoms,

while a pre-symptomatic case would test positive before developing a cough or a fever.

That is….if we're testing at all.

In COVID-19's case, preliminary data out of Singapore suggests that presymptomatic

cases are contributing to the spread of this disease, while here in the U.S., the head

of the CDC recently suggested that asymptomatic cases could make up as many as 25% of the total infections.

But because the person has no symptoms, they don't realize they shouldn't be going out,

they shouldn't be interacting with others.

And that stealthiness of it, the ability to transmit without symptoms, is part of what

is causing this pandemic to occur.

There are data to show that even before individuals have symptoms there's a lot of virus in the body.

What we call a high viral load.

And the more virus there is in the body, the more easily that virus can be generated in

droplets and spread to other individuals.

That's part of why testing is so important.

Right now, it's believed that it takes on average 5-6 days after exposure, and sometimes,

up to 14 before symptoms begin.

So that's why measures like social distancing and hand washing are so crucial to stem the

spread of COVID-19, especially when you're dealing with a virus that has a higher rate of transmission, or “R nought,” than the flu:

Influenza is typically a little bit more than one.

Based on early studies, the R nought reproduction number for COVID is about two and a half.

So for every one person infected, somewhere between two to three new infections incur.

COVID-19's stealthy nature makes it unlike anything we've ever seen.

And we know that with all the information out there, it can feel overwhelming.

But from vaccine development to antiviral therapy to advanced contact tracing and testing

strategies, the world at large is better scientifically equipped than ever before.

It might take a little while, but we can tackle this unprecedented challenge, and it all starts with you.

There's nothing easy about a pandemic.

The hardest thing, I think, for health care workers and people in general, is the scope of the disease.

Society is not used to something like that.

You have an active role to play by staying at home, by washing your hands, and by helping

other people to stay at home and be isolated if they're sick.

So I just want to thank everybody for doing their part to help us all get through this pandemic.