What began with a handful of mysterious illnesses in a vast central China city has traveled the world, jumping from animals to humans and from obscurity to international headlines. First detected on the last day of 2019, the novel coronavirus has infected tens of thousands of people — within China’s borders and beyond them — and has killed more than 2,500. It has triggered unprecedented quarantines, stock market upheaval and dangerous conspiracy theories.
Most cases are mild, but health officials say the virus’s spread through the United States appears inevitable. As the country and its health-care system prepares, much is still unknown about the virus that causes the disease now named covid-19.
The Washington Post has spoken to scores of doctors, officials and experts to answer as many of your questions as we can about the newest global health emergency. Here’s what we know so far.
What is it?
These days, “coronavirus” is often prefaced with the word “novel,” because that’s precisely what it is: a new strain in a family of viruses we’ve all seen before — and, in some form, had. According to the WHO, coronaviruses are a large family of viruses that range from the common cold to much more serious diseases. These diseases can infect both humans and animals. The strain that began spreading in Wuhan, the capital of China’s Hubei province, is related to two other coronaviruses that have caused major outbreaks in recent years: severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS).
Symptoms of a coronavirus infection range in severity from respiratory problems to cases of pneumonia, kidney failure and a buildup of fluid in the lungs.
How deadly is it?
Public health officials say the novel coronavirus is less deadly than SARS, which killed about 10 percent of people who were infected during the outbreak that began in 2002. But epidemiologists are still trying to determine exactly how deadly covid-19 is.
About 2 percent of reported cases have been fatal, but many experts say the death rate could be lower. That’s because early in an outbreak, mild illnesses may not be reported. If only people with severe illness — who are more likely to die — seek care, the virus will appear much more deadly than it really is because of all the uncounted people with milder symptoms.
Early in the outbreak, one expert estimated that although 2,000 cases had been reported, 100,000 people probably were sick. Under counting cases can artificially increase the infection’s mortality rate.
How does it spread?
Covid-19 spreads more easily than SARS and is similar to other coronaviruses that cause cold-like symptoms, experts have said. It appears to be highly transmissible, and since cases are mild, the disease may be more widespread than current testing numbers suggest.
There have been reports of people transmitting the virus before they show symptoms, but most experts think this is probably not a major driver of new infections. What is concerning, however, is that symptoms can be mild, and the disease can clearly spread before people realize they’re sick. SARS spread when people had full-blown illness, which is one reason it was possible to contain it — it was easier to tell who had the virus.
A report in the New England Journal of Medicine suggested covid-19 reaches peak infectiousness shortly after people start to feel sick, spreading in the manner of the flu. A study published in JAMA chronicled the case of a 20-year-old Wuhan woman who appeared to infect five relatives, even though she never showed signs of illness.
Who is most at risk of severe illness?
Similar to other respiratory illnesses, older people and those with illnesses such as diabetes and high blood pressure are at increased risk. Early studies have also suggested men are at greater risk.
But, as with other diseases, there can be tremendous individual variation in how people respond. There will be people with known risk factors who recover as well as people who develop severe cases for reasons we don’t understand.
“It may be a very specific thing about the way your immune system interacts with a particular pathogen,” said Allison McGeer, an infectious-disease epidemiologist at the University of Toronto. “It may also be just about exactly what your exposure is.”