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March 18, 2020 6 min read

What symptoms are most common, which groups are most at risk, and more?

The outbreak of Covid-19, a coronavirus-caused illness that originated in Wuhan, China, and has since spread to most of the world, is one of the most serious public health crises in decades. It has spread far wider than Ebola did in 2014, and the World Health Organization has designated it a pandemic. Johns Hopkins’s tracker is worth bookmarking with case number counts in the US and worldwide as the crisis progresses.

The situation on the ground is evolving incredibly quickly, and it’s impossible to synthesize everything we know into clean, intelligible charts. But we do know a fair bit about how bad the outbreak is, what the disease does, and what controlling and ultimately ending the outbreak will look like.

With that in mind, here are nine charts that help explain the Covid-19 coronavirus crisis.

1) The virus is spreading rapidly

The confirmed Covid-19 caseload has risen rapidly day today, but here’s where things stood as of March 15. This is almost certainly a substantial underestimate, as testing capacity varies widely from country to country and many if not most people infected with the virus have not been diagnosed yet.

Many of the reported cases are still from the earlier peak in China. But while the number of new cases in China has fallen, the number of new international cases is rising, indicating that the epicenter of the problem has shifted from China to new places like Europe and the United States.

Note that the huge spike in new cases was due to improved data reporting from China; there was no one particularly bad day in the middle of February.


2) Know the symptoms

The symptoms of Covid-19 vary from case to case, but the most common ones in China, from February data, are fever and dry cough (which are each seen in a majority of cases), fatigue, and sputum (the technical term for thick mucus coughed up from the respiratory tract).

3) This is much more severe than an ordinary flu

This is much more severe than an ordinary flu

It is tempting to compare Covid-19 to a more familiar disease: the seasonal flu. After all, the flu also has mild symptoms for most people and can be dangerous and lethal among vulnerable populations like the elderly. President Trump even made this comparison recently.

But as the case-fatality data shows, there’s no real comparison. About 6 percent of people 60 or older infected with Covid-19 die, according to the data from China we have so far; that’s over six times the fatality rate in the US for older people infected with the flu. The overall Covid-19 fatality rate maybe 12 to 24 times the flu death rate. (Estimates for the fatality rate for Covid-19 vary, and they vary by region depending on the response to the outbreak.)

4) Experts also think Covid-19 is more contagious than the ordinary flu

 Experts also think Covid-19 is more contagious than the ordinary flu

There’s another way that Covid-19 is a tougher adversary than the seasonal flu: Its R0 (“R naught”) is over 2, indicating that it’s more contagious than the typical flu. R0 estimates the number of people an average infected person spreads the disease too. “R0 is important because if it’s greater than 1, the infection will probably keep spreading, and if it’s less than 1, the outbreak will likely peter out,” the Atlantic’s Ed Yong explains. Covid-19’s R0 is substantially higher than 1, giving more reason for concern.

5) Older people in China have been at the greatest risk of dying from Covid-19

Older people in China have been at the greatest risk of dying from Covid-19


The Spanish flu of 1918-’19, the most horrific pandemic in modern times, focused mainly on the young. It had biological similarities to a flu pandemic in the 1830s that gave some older people in the 1910s limited immunity.

Covid-19 is not like that. So far, deaths in China have been concentrated among older adults, who have weaker immune systems on average than younger people and have a higher rate of chronic illness. People of all ages with chronic medical conditions are also at higher risk. The risk of death is real for younger people as well, but older people are most at risk.

6) Death rates in China have declined over time

Death rates in China have declined over time

One glimmer of hope in this story is that Chinese medical authorities appeared to get better at treating infections and preventing death as the outbreak proceeded. “Even the first and hardest-hit province, Hubei, saw its death rate tumble as public health measures were strengthened and clinicians got better at identifying and treating people with the disease,” Vox’s Julia Belluz explains.

The rate didn’t go down on its own; China took drastic, even authoritarian measures to lock down affected areas and contain the virus’s spread so that the medical system was not overwhelmed.


7) But the US pandemic is looking like Italy’s so far

But the US pandemic is looking like Italy’s so far

This chart, adapted by my colleagues Dylan Scott and Rani Molla from work by John Burn-Murdoch of the Financial Times, compares how the confirmed caseload in each country has evolved since the 100th case. Note that the scale is logarithmic: 10,000 is as far from 20,000 as it is from 5,000. Straight lines actually show exponential growth.

Singapore and Hong Kong seem to have managed slow exponential growth, as has Japan to a degree. But the US seems to be following the trajectory of Italy, whose outbreaks have forced the country to adopt a dramatic quarantine policy, and Iran, which has declined a quarantine and is only seeing worsening outcomes. The good news is that South Korea was on this trajectory too but appears to have slowed the disease’s spread; time will tell if South Korea is able to maintain those results, or if it faces another wave of the virus.

8) The US is not testing enough people

The US is not testing enough people

The Trump administration’s slow rollout of testing for coronavirus has become something of a national scandal, and it’s easy to see why when you compare the US testing rate to that of other affected countries. South Korea stands out for its rapid rollout of extensive testing, including through innovative drive-through testing programs.

Drive-through testing is being piloted in some parts of the US, like New Hampshire, but we still have a long way to go before we match South Korean and Chinese testing levels. For the most up-to-date data on this issue, check here.

9) Why canceling events and self-quarantining is so important

Why canceling events and self-quarantining is so important


Covid-19 has quickly made large-scale gatherings and conferences unpopular if not socially frowned upon. This change arrived quickly and may seem jarring, but it’s easier to see the logic when you understand the theory behind this kind of “social distancing” policy. The key is to “flatten the curve”: slowing the rate of increase in infections so that you spread out the cases, even if the total number doesn’t change.

Flattening the curve slows the rate at which new cases arrive in hospitals, easing the burden on health care infrastructure and improving the odds that individual patients will survive.

10) Social distancing really works to flatten the curve

Social distancing really works to flatten the curve

This chart, building on a model by entrepreneur Tomas Pueyo, is a potent illustration of how social distancing — avoiding bars/restaurants and big gatherings, staying inside and working from home if at all possible, etc. — right now can help “flatten the curve” and slow the virus’s growth. The chart compares how a single day’s delay in social distancing can increase the peak of the outbreak significantly, by 40 percent using the parameters Pueyo opted for. Note that this is merely a theoretical projection, but we need to rely on theory to generate predictions during fast-moving crises like this. For more, see Umair Irfan’s piece here.

11) Just because you don’t feel sick doesn’t mean you’re safe to move around

Just because you don’t feel sick doesn’t mean you’re safe to move around

Social distancing isn’t just about protecting yourself. It’s primarily about protecting other people by slowing transmission. To see how this works, consider the above chart showing the March 10 estimate by a group of scientists, published in the Annals of Internal Medicine, of the incubation period of the virus.

As Vox’s Brian Resnick explains, “you can see that nearly everyone who develops symptoms of Covid-19 shows them around 10 to 15 days after the infection, and the majority get symptoms by around five days.” That means that many patients are asymptomatic for days after being infected. That means that “not feeling sick” isn’t a good enough reason to break social distancing norms. You could just be incubating the virus and spreading it inadvertently.