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Last updated November 23, 2020. 6 minute read

The COVID-19 dictionary

Here you’ll find some of the most common terms you’ll see used in stories about coronavirus disease 2019 (COVID-19) and what they mean.

Written by Health Guide
Reviewed by Dr. Mike Bohl, MD, MPH

The rapid spread of coronavirus disease 2019 (COVID-19) has been accompanied by a flurry of information. It can be a lot to process—not just the latest recommendations about lifestyle changes to slow the spread, but the fundamentals of the disease itself. These are some of the most common terms you’ll see used in stories about the coronavirus and what they mean.

Antibodies. Antibodies (also called immunoglobulins) are an important part of the immune system. When the body is infected with an infectious agent (such as a virus or bacterium), the body produces antibodies to it. The antibodies then help the body fight the infectious agent. A COVID-19 antibody test (also called a serologic test) is a blood test that looks for antibodies to COVID-19, to see if you have been exposed to the virus in the past.

Asymptomatic. To be asymptomatic means that you show no symptoms. After becoming infected with COVID-19, the average person may be asymptomatic for up to 5.1 days and 97.5% of people may be asymptomatic for up to 11.5 days. However, it is important to remember that you can still transmit and spread the virus when you are asymptomatic.

The Centers for Disease Control and Prevention (CDC). A federal agency that was founded in 1946 and is responsible for limiting and preventing disease, injury, and disability in the United States and abroad. For recommendations about what you should do during the COVID-19 pandemic, consult the CDC website.

Cluster. An unusually high number of disease cases in a close geographical area at the same time. The first COVID-19 cluster in the United States was in a nursing home outside of Seattle.

Community spread. When a disease is spread from person-to-person in the community. People who are newly infected may not know when or where they were infected. This is different from diseases that do not transmit person-to-person.

Contagious. Able to spread disease by direct or indirect contact. Researchers believe that people can transmit the novel coronavirus for days before they show symptoms and that people are most contagious before and during the first week of symptoms.

Containment. To limit the spread of a disease to one geographic area. Attempts to contain the virus that causes COVID-19 failed, allowing it to spread internationally. Governments are now in the mitigation phase of the pandemic, attempting to reduce impact by slowing the spread.

Coronavirus. A family of viruses named for the distinctive spikes on their surface. Coronaviruses cause a variety of respiratory illnesses including SARS, MERS, COVID-19, and the common cold.

Coronavirus disease 2019 (COVID-19). COVID-19 is the name of the disease that is currently a global pandemic. It is caused by the virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The disease produces mild flu-like symptoms in approximately 81% of cases. In the remainder, it can cause severe symptoms requiring hospitalization. In some cases, the disease may necessitate mechanical ventilation and can even lead to death.

Droplets. Respiratory droplets are produced when a person coughs or sneezes. The droplets are how coronavirus is transmitted. They can land in the mouths or noses of people nearby and be inhaled into the lungs.

Endemic. Endemic diseases are diseases that are always present in a given population at an expected/consistent level. An example of an endemic disease in the United States is chickenpox. Similar but different terms are “epidemic” (which refers to a disease that spreads more than expected in a given population) and “pandemic” (which refers to an epidemic that spreads across multiple continents or around the world).

Epidemic. An epidemic is an increase in the number of cases of a disease beyond what is expected in a given population. Similar but different terms are “endemic” (which refers to a disease that is always present in a population at an expected level) and “pandemic” (which refers to an epidemic that spreads across multiple continents or around the world).

Flatten the curve. Reducing the immediate spread of disease to prevent a spike in cases, which can overwhelm healthcare systems. To “flatten the curve” would distribute potential cases of the disease over a longer period of time, increasing the chances that enough resources will be available to treat them all. This is particularly important during the current coronavirus crisis. Of note, “flattening the curve” does not necessarily reduce the total number of people who will contract a disease. Instead, it spreads out the timeline.

Incubation period. The amount of time between a person being infected with a disease and when he or she begins to show symptoms. Also known as the latency period, this is when a person may be infectious to others without knowing it. The median incubation period for COVID-19 is estimated to be between five and 12 days.

Influenza. Also known as “the flu,” influenza is a respiratory illness caused by one of several influenza viruses (influenza A and influenza B). Symptoms of the flu include fever, cough, fatigue, and body aches. The flu can cause complications and can be fatal for people who are elderly or immunocompromised. Flu viruses mutate over time, and new forms of the flu have caused outbreaks and pandemics throughout history including the 1918 Spanish flu, the 1968 Hong Kong flu, and the 1976 swine flu. Some flu symptoms are similar to COVID-19 symptoms. Read more about the signs and symptoms of coronavirus, here.

Isolation. Isolation is a public health technique used to help prevent the spread of disease. People who are diagnosed with a disease are separated from the general population so they can’t infect other people. Isolation is different from quarantine, which is the separation of healthy people who have been exposed to (but do not yet have) a disease.

Lockdown. “Lockdown,” “shelter-in-place,” and “stay-at-home” are different types of orders that many governments put in place to reduce the spread of COVID-19. These orders vary by location but often include limiting nonessential travel, closing schools, closing public spaces (such as bars, restaurants, nightclubs, and gyms), and encouraging or mandating people to stay at home except in certain circumstances. Unlike “isolation” (which is intended for infected people) and “quarantine” (which is intended for exposed people), lockdown orders are more widespread and are intended to be followed by everybody.

Middle East respiratory syndrome (MERS). This is a respiratory disease caused by a type of coronavirus that was first reported in Saudi Arabia in 2012. Its symptoms include fever, cough, and shortness of breath. According to the CDC, it is fatal in 30% to 40% of cases. Only two people tested positive for MERS in the US, both in 2014.

Mitigation. To reduce the impact of something. Because COVID-19 could not be contained, countries are now in the mitigation phase, hoping to slow its spread so health systems aren’t overwhelmed with cases at one time. 

National emergency. President Trump declared the COVID-19 pandemic to be a national emergency on March 14. The declaration unlocked federal disaster relief funding, to be distributed to state and local governments to combat the virus.

Novel. “Novel” is another word for “new.” COVID-19 is referred to as being caused by a novel coronavirus because the specific virus had not been seen in humans before the current pandemic.

Outbreak. An outbreak is a sudden occurrence of a disease in a given population.

Pandemic. A pandemic refers to the situation in which an infectious disease spreads across multiple continents or across the world. Notable pandemics include COVID-19, certain strains of the flu, cholera, and HIV. Similar but different terms are “endemic” (which refers to a disease that is always present in a population at an expected level) and “epidemic” (which refers to a disease that spreads more than expected in a given population).

Person-to-person. Transmission of disease from one human to another. The first case of person-to-person transmission of the COVID-19 virus in the US is believed to be between a woman who traveled to China and her husband upon returning.

Quarantine. Quarantine is a public health technique used to help prevent the spread of disease. People who have been exposed to a disease are separated from the general population, to see if they eventually develop the disease. Quarantine is different from isolation, which is the separation of people who have actually been diagnosed with a disease.

Serologic test. See “Antibodies.”

Severe acute respiratory syndrome (SARS). This is a respiratory disease caused by a type of coronavirus that was first reported in China in 2002. Like COVID-19, SARS could cause severe respiratory problems and death. It was quickly contained. No cases of transmission have been reported since 2004.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This is the name of the virus that causes COVID-19. SARS-CoV-2 is in the family of viruses called coronaviruses. It is related to other viruses, such as the ones that cause SARS, MERS, and the common cold.

Self-quarantine. “Self-quarantine” is similar to “quarantine,” but it is not mandated. People who think they have been exposed to a contagious disease are advised to voluntarily separate themselves from others and limit their movement, to see if they become sick. Individuals who have been exposed to COVID-19 are encouraged to self-quarantine for 14 days.

Shelter-in-place. See “Lockdown.”

Social distancing. To maintain a distance between yourself and other people. Experts advise not gathering in groups of more than 10 people and not coming within six feet of others. Unlike isolation and quarantine, social distancing does not necessarily require you to stay in one place.

Stay-at-home. See “Lockdown.”

Symptomatic. Showing symptoms of a disease or condition.

Wuhan. The capital city of the central Hubei province in China, where COVID-19 was first reported. On Dec. 31, 2019, China alerted the World Health Organization (WHO) to a number of unusual cases of pneumonia in Wuhan. Several were traced to workers at the Huanan Seafood Wholesale Market.

Vaccine. Vaccines are treatments that help the body develop immunity against infectious agents, like viruses and bacteria. After receiving a vaccine for a specific infectious agent, the body produces antibodies. Then, if the body encounters the infectious agent in the future, the antibodies help fight it. There are more than 50 candidate vaccines, some of which have even begun testing in human subjects. But even if these trials are successful, a vaccine won’t be available for widespread use before the end of the year, says Dr. Anthony Fauci of the US National Institutes of Health. 

Zoonotic. An infectious disease that originated in animals and spread to humans. SARS-CoV-2, the virus that causes COVID-19, is believed to have originated in animals and spread to humans. Read about pets and COVID-19 here.