Coronavirus glossary
Get definitions of unfamiliar words you may be hearing during the coronavirus pandemic.
COVID-19
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.
Virus
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.
Bacteria
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
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
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.
Epidemic
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.
Pandemic
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.
Vaccine
Vaccines are substances that prevent the spread of disease. They can be given in a shot, by mouth, or by a nose spray.
Most vaccines work like this: When people are vaccinated against a disease like the flu or chicken pox, 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.
The Pfizer and Modena COVID-19 vaccines are a new kind of vaccine called messenger RNA, or mRNA. These new mRNA vaccines teach our cells how to make a protein that protects us from getting infected. Unlike the other kind of vaccines, the new ones do not use any live virus. Instead, they deliver instructions to our cells to make the protein. Once the cells have that protein, they use it to make antibodies, which protect against future infection.
Two doses of this type of vaccine are needed for it to work properly against COVID-19. Both Pfizer and Moderna have been proven safe for most adults, and Pfizer is now approved for kids 12 and older. More testing is going on now so that younger kids can be vaccinated soon. Experts think a safe and effective vaccine for kids five to 11 could be ready later this year.
Researchers have been developing mRNA vaccines for many years. Thanks to that head start, they were able to use what they already know about other viruses to quickly develop and test the COVID-19 vaccine.
This story has been updated with new information about vaccines for children.