A novel respiratory virus that originated in Wuhan, China, last December has spread to six continents. Hundreds of thousands have been infected, at least 20,000 people have died and the spread of the coronavirus was called a pandemic by the World Health Organization in March.
Much remains unknown about the virus, including how many people may have very mild or asymptomatic infections, and whether they can transmit the virus. The precise dimensions of the outbreak are hard to know.
Here’s what scientists have learned so far about the virus and the outbreak.
What is a coronavirus?
Coronaviruses are named for the spikes that protrude from their surfaces, resembling a crown or the sun’s corona. They can infect both animals and people, and can cause illnesses of the respiratory tract.
At least four types of coronaviruses cause very mild infections every year, like the common cold. Most people get infected with one or more of these viruses at some point in their lives.
Another coronavirus that circulated in China in 2003 caused a more dangerous condition known as Severe Acute Respiratory Syndrome, or SARS. The virus was contained after it had sickened 8,098 people and killed 774.
Middle East Respiratory Syndrome, or MERS, first reported in Saudi Arabia in 2012, is also caused by a coronavirus.
The new virus has been named SARS-CoV-2. The disease it causes is called Covid-19.
How dangerous is it?
It is hard to accurately assess the lethality of a new virus. It appears to be less often fatal than the coronaviruses that caused SARS or MERS, but significantly more so than the seasonal flu. The fatality rate was over 2 percent, in one study. But government scientists have estimated that the real figure could be below 1 percent, roughly the rate occurring in a severe flu season.
About 5 percent of the patients who were hospitalized in China had critical illnesses.
Children seem less likely to be infected with the new coronavirus, while middle-aged and older adults are disproportionately infected.
Men are more likely to die from an infection compared to women, possibly because they produce weaker immune responses and have higher rates of tobacco consumption, Type 2 diabetes and high blood pressure than women, which may increase the risk of complications following an infection.
“This is a pattern we’ve seen with many viral infections of the respiratory tract — men can have worse outcomes,” said Sabra Klein, a scientist who studies sex differences in viral infections and vaccination responses at the Johns Hopkins Bloomberg School of Public Health.
How is the new coronavirus transmitted?
Experts believe that an infected animal may have first transmitted the virus to humans at a market that sold live fish, animals and birds in Wuhan. The market was later shut down and disinfected, making it nearly impossible to investigate which animal may have been the exact origin.
Bats are considered a possible source, because they have evolved to coexist with many viruses, and they were found to be the starting point for SARS. It is also possible that bats transmitted the virus to an intermediate animal, such as pangolins, which are consumed as a delicacy in parts of China, and may have then passed on the virus to humans.
The outbreak grew because of human-to-human transmission.
People infected with the virus produce tiny respiratory droplets when they breathe, talk, cough or sneeze, allowing the virus to travel through the air.
Most respiratory droplets fall to the ground within a few feet. People who are in close contact with those infected, particularly family members and health care workers, may catch the virus this way.
Scientists don’t know how long the new coronavirus can live on surfaces, and preliminary research suggests that hot and humid environments may not slow down the pathogen’s spread. Warm weather does tend to inhibit influenza and milder coronaviruses.
Infected people may be able to pass on the new coronavirus even…
Read More: What is Coronavirus? – The New York Times