How long will social distancing last? It's complicated.

• To prevent the spread of the COVID-19 coronavirus and flatten the curve, many countries are practicing social distancing, or what the WHO is now calling physical distancing.
• But how long will this period of social distancing last?
• Unfortunately, no one knows for sure. The answer is complicated, and it partly depends on our actions.
• Visit Business Insider's homepage for more stories.

Following is a transcript of the video.

Narrator: You've probably been told to stay indoors, limit contact, and go outside only for essential activities. All because of this curve.

Clip: Flatten the curve.

Clip: The curve.

Clip: The curve.

Clip: This curve.

Clip: Flattening the curve.

Narrator: It shows the hypothetical number of cases in a pandemic over time without an intervention and with an intervention. The dotted line represents the capacity of hospitals and healthcare systems. If social distancing goes well, this curve will be flattened, allowing hospitals to take in and discharge patients without being overwhelmed. The result? More people will get access to the healthcare and attention they need, and, hopefully, fewer people will die. But the x-axis represents the time since the first case. If you lower the peak, the pandemic might last longer, because the number of new cases will be spread out over a longer period of time. But the question on a lot of people's minds is exactly how long will that be? Right now, the world is trying to both flatten and shorten the curve. Fewer cases and a shorter outbreak. But to do that, we might need to live like this for a while. To understand why we are social distancing, or what the World Health Organization now calls physical distancing, we need to explain how easily the coronavirus spreads.

Aylin Woodward: In order to best understand how contagious an infectious disease is, experts look to a critical metric called the R0 value. So, that's basically the average number of people that one sick person can go on to infect in a group that has no immunity to a virus.

Narrator: The R0 of the coronavirus is thought to be between two and 2.5. That means that each person with the virus could infect about 2.2 other people.

Lauren Ancel Meyers: And we also believe that it is possible for people to be spreading this disease even before they're feeling sick. So, we call that presymptomatic transmission. So, all that taken together means that this thing spreads quite quickly and sometimes silently.

Narrator: For comparison, the R0 of the flu is about 1.3. 1.3 sounds close to 2.2, but the difference can be huge. Someone with the flu might pass it on to dozens of people. But someone with the coronavirus might indirectly pass it on to thousands. R0 isn't a fixed number, but it does indicate how quickly the virus is spreading.

Woodward: A lower R0 means an outbreak is slowing or stopping, while a higher one means it's swelling.

Narrator: As the US tests more people, the number of cases will continue to increase, allowing us to see the spread of the virus as it stands. If we slow the transmission of the virus, we lower the R0, and eventually we will get from this part of the curve to that. And with no vaccine, our best solution is social distancing.

Ancel Meyers: Anything you do that brings you in contact with other people is a possible point of transmission. Narrator: This is why we're seeing so many events get canceled or postponed.

Ancel Meyers: The earlier you enact these measures, the more rapidly you can reduce the transmission rate.

Narrator: The faster we get to the point of reducing the transmission rate, the faster we could get to the end of the outbreak, essentially not just flattening the curve, but making it smaller. But if you wait until everyone around you is sick, it'll be too late.

Aria Bendix: There's still time to contain this outbreak, and that's why we are all inside, because it's still possible to get this under control.

Narrator: Testing will catch people who are sick enough to go to the hospital, but not necessarily people who have mild or no symptoms. And those people could still spread to that average 2.2 other people. To prevent this, many states have issued stay-at-home orders, which allow only essential businesses like grocery stores and pharmacies to remain open. But how long will things be like this?

Ancel Meyers: It's hard to project what's going to happen, because the course of these outbreaks is really going to depend on the measures that we take as communities.

Narrator: The truth is no one actually knows how long we will have to social distance. You can't see the peak of the curve when you're still on the upward slope. And each state is handling things differently. Illinois' stay-at-home order is expected to be in effect until April 7. But in some states, like California and New York, there is no projected end date. On March 15, the CDC advised against gatherings of 50 or more people for eight weeks. And many universities have told students that the rest of the semester will be online. But some officials stress that things could be like this for even longer.

Andrew Cuomo: You're not going to turn on the news tomorrow morning and they're going to say, "Surprise, surprise, this is all now resolved in two weeks." That is not going to happen.

Bendix: Ultimately, experts say that those social-distancing measures will sort of be necessary until we have a vaccine, and that's 12 to 18 months. So that's sort of at the very far end of things, but that doesn't necessarily mean we're all in our homes for 18 months, it means maybe we're avoiding public gatherings for that amount of time or limiting the amount of travel internationally, but it's not necessarily as restrictive as what we're seeing now.

Woodward: There's no magic number that suddenly shows you're on the downturn of an epidemic growth curve. However, by tracking the number of new cases per day and by seeing that number decrease consistently over time, I think that's really a good litmus test for knowing that perhaps the peak is behind you.

Narrator: We've seen other countries, like China and South Korea, dramatically lower the number of daily reported cases after implementing broad testing and social-distancing measures. But it's important to note that some experts think there could be another round of social distancing.

Bendix: We start letting people go back to work, go back to school, and then once that happens, the virus would have an opportunity to spread again and there would be a second wave of infection.

Narrator: If we end social distancing too soon, new cases could pop up and we could end up in another curve again. If the number of reported cases spikes again, we might have to enact the same policies we have in place now, which might be stressful to hear. But it's important to stay calm and follow the advice of healthcare professionals.

Ancel Meyers: When you take measures to prevent yourself from getting infected or spreading the disease to others, you may be indirectly saving other people's lives.

Narrator: Right now, the US is still on the upward slope of the curve. But we won't be forever. And all of our actions can directly affect the slope of that curve.