From left: Colorized transmission electron micrograph of herpes simplex virus, Ebola virus and SARS-CoV-2 virus particles. Researchers now believe the coronavirus is likely to be a continuing threat until a vaccine is developed. NIAID; NIH; NIH hide caption
A recovered coronavirus patient takes a selfie before being discharged from a hospital in Sri Lanka. Researchers are trying to determine whether having a case of COVID-19 will give you immunity. Xinhua News Agency/Getty Images hide caption
School was suspended for six weeks in Hong Kong as part of the strategy to keep SARS from spreading. On May 12, 2003, primary school children returned to class amid signs that the outbreak was coming under control. Bobby Yip/Reuters hide caption
Making sure to frequently give your hands a thorough scrub — with soap and for about as long as it takes to sing the "Happy Birthday" song a couple of times — can significantly cut your chances of catching the flu or other respiratory virus. Mandel Ngan/AFP via Getty Images hide caption
This transmission electron microscope image shows SARS-CoV-2, the virus that causes COVID-19, isolated from a patient in the U.S. Virus particles are shown emerging from the surface of cells cultured in the lab. The spikes on the outer edge of the virus particles give coronaviruses their name, crown-like. NIAID-RML/NIH/Flickr hide caption
A visualization of the SARS virus. It is a type of coronavirus and displays the coronavirus' signature crownlike appearance under a microscope. 3D4MEDICAL/3D4MEDICAL hide caption
Hospital staff wash the emergency entrance of Wuhan Medical Treatment Center, where patients infected with a new virus are being treated, in Wuhan, China, on Wednesday. Dake Kang/AP hide caption
Staff in biohazard suits hold a metal stretcher on Tuesday by the inpatient department of Wuhan Medical Treatment Center, where some people infected with a novel coronavirus are being treated in China. Dake Kang/AP hide caption
A man rides past the Huanan Seafood Wholesale Market in Wuhan, China, which was closed after being linked to cases of a newly discovered coronavirus. Getty Images hide caption
Three U.S. airports will screen passengers from Wuhan, China, for coronavirus symptoms: Los Angeles International Airport (pictured above), JFK in New York and SFO in San Francisco. FG/Bauer-Griffin/GC Images hide caption
Health workers killed chickens in a Hong Kong market in 2014 in an effort to stop the spread of H7N9 flu. It's being watched closely as a virus that might spark a pandemic outbreak. Vincent Yu/AP hide caption
Each year thousands of people from around the world tour the Gomantong Cave in Borneo. Although scientists have found a potentially dangerous virus in bats that roost in the cave, no one has ever gotten sick from a trip here. Razis Nasri hide caption
The Middle East respiratory syndrome coronavirus, which causes MERS, is one of the microbes that has sparked research controversy. NIAID/CDC hide caption
A transmission electron micrograph shows Middle East respiratory syndrome coronavirus particles (colorized yellow). NIAID hide caption
The coronavirus responsible for Middle East respiratory syndrome (green particles) seen on camel cells in a scanning electron micrograph. NIAID/Colorado State University hide caption