This is what doctors and scientists have named the disease that most people refer to as “coronavirus,” the disease that started spreading around the world in December 2019. The name COVID-19 is a mash-up of several words. The first is "corona" (CO), which means "crown" in Latin; coronaviruses are named for the crown-like spikes on their surface. The other words are "virus" (VI) and "disease" (D). The "19" comes from the year 2019, when the disease was first discovered.
The term "coronavirus" actually refers to a family of viruses that causes many different types of diseases, including the common cold. COVID-19 is a "novel coronavirus," which means it’s a new disease unfamiliar to scientists and doctors. Learn more about the coronavirus and staying safe.
Viruses are tiny organisms that are so small that they can’t be seen without special microscopes. These microorganisms are found all around us—in dirt, water, and in the air. Viruses can't survive for long outside of a living host (meaning a person, plant, or animal) because they need a host’s energy to grow. Once inside a host, a virus can multiply and attack cells, causing diseases such as the flu, chicken pox, and COVID-19.
Like viruses, bacteria are also microorganisms and can be found all around us (though they’re a little bigger than viruses). Unlike viruses, bacteria can live almost anywhere, including in or on our bodies. (If you’ve ever had an ear infection or strep throat, you’ve had a bacterial infection.)
While most viruses cause disease, less than one percent of bacteria does. Most bacteria are good for our health and Earth’s. In fact, lots of helpful bacteria actually live in us, including at least 500 species in your large intestine. They help break down food and even create nutrients like vitamin K. Other bacteria are responsible for things like morning breath and cavities. Learn more about the things that live on you.
Infection occurs when a virus, bacteria, or other disease-causing microorganism enters a human’s body and begin to multiply. These microorganisms are often transmitted by little droplets from coughs or sneezes, which is why doctors say you should always cover your mouth with your elbow when you cough or sneeze. You could also pick up the microorganisms by touching doorknobs or countertops that an infected person has touched, and then touching your eyes, nose, or mouth. That’s why the best protection from disease-causing microorganisms is to wash your hands frequently and keep your fingers away from your face.
Disease occurs when cells in the body are damaged as a result of the infection, and symptoms, or signs of an illness, begin to appear. Symptoms can include a sore throat, chills, vomiting, and more. Symptoms of COVID-19 might include a dry cough, a fever, and shortness of breath.
An epidemic is a sudden increase in the number of people in a certain area—like a town, city, or state—with the same disease. For instance, doctors expect a certain amount of people in certain areas to have the flu every year. But if that number suddenly goes up by a lot, it becomes a flu epidemic.
A worldwide outbreak of a disease is called a pandemic. Pandemics happen when a virus spreads easily and infects a lot people. The current COVID-19 outbreak is a pandemic.
Vaccines are substances that prevent the spread of disease. They can be administered in a shot, by mouth, or by a nose spray. When people are vaccinated against a disease, they are purposely given a dead or weakened amount of the bacteria or virus that causes the disease. It’s a small enough amount that it causes little to no sickness in the person who receives it. Instead, it causes the person’s immune system to make antibodies, or proteins that fight disease. This means if a larger amount of the same bacteria or virus enters the person’s body later, their immune system will be prepared to fight it. Vaccines prevent many kinds of diseases, such as chicken pox and the flu. Scientists and researchers are currently working hard to develop a vaccine against COVID-19.
BACTERIA: STEVE GSCHMEISSNER, SCIENCE PHOTO LIBRARY / GETTY IMAGES; EBOLA: CALLISTA IMAGES, GETTY IMAGES; VACCINE: JGI, TOM GRILL / GETTY IMAGES