COVID-19 Glossary

We are still learning new information about COVID-19. You may be hearing some unfamiliar phrases, such as PPE, herd immunity and mRNA. In an effort to make this ever-evolving situation a little bit easier to understand, here is a glossary explaining a list of terms related to COVID-19.


When a patient is a carrier of an illness, but does not show any signs or symptoms of the illness.

Community transmission

Community transmission occurs when a disease, such as COVID-19, is transmitted within and throughout a community, rather than just from a high-risk area or population.

Contact tracing

A measure being used by public health officials, including in Connecticut, to help slow the spread of COVID-19. Patients who test positive for the virus are contacted to determine all of the people they’ve had close contact with. Then, those individuals are warned about their potential exposure and given information about the next steps they should take.


Coronaviruses are a group of viruses that are common in both humans and animals that usually cause mild to moderate respiratory illnesses.


The spread of a disease over a wide area, impacting many people at the same time.


In medicine, epidemiology is the method used to determine the causes of diseases. 

“Flatten the curve”

The number of COVID-19 cases is expected to go up, resulting in a sharp rise if mapped out over time. When there’s a surge of patients to hospitals, we can help “flatten the curve” by slowing down the spread of cases and allowing the healthcare capacity and resources to treat and manage the demand of ill patients.


When a person is infected with COVID-19 and the flu at the same time.

Hand hygiene

Wash your hands with soap and water for at least 20 seconds or more, or by using an alcohol-based hand sanitizer that is at least 60% alcohol by content. Practicing proper hand hygiene can help prevent the spread of germs and decrease community transmission of contagious illnesses.

Herd Immunity 

When a significant portion of the population is immune from an infectious disease, the spread of the illness is not likely. "Herd immunity" can help to protect people who cannot be vaccinated, such as newborn babies. However, it is not a replacement for a vaccine.


Patients who have a weakened immune system are immunocompromised, making it more difficult for them to fight infections or disease.

Incubation period

The time from exposure to a contagion (such as COVID-19) to when a patient starts to show signs and symptoms.


Isolation is when someone who is sick stays away from others to prevent them from getting sick.  This includes sleeping in a separate bedroom and using a separate bathroom whenever possible. 

mRNA vaccines

The Pfizer and Moderna COVID-19 vaccines are mRNA vaccines. They consist of genetic material called messenger RNA, or mRNA, that stimulates the immune system to make antibodies that protect against COVID-19.


Personal protective equipment, or PPE, is used by healthcare workers to protect themselves when treating patients. PPE recommended for the care of a COVID-19 patient includes gloves, a gown, face shield and N95 respirator. 


The World Health Organization defines a pandemic as a worldwide spread of a new disease. Past pandemics include the 1918 influenza pandemic and the H1N1 pandemic of 2009.


A quarantine restricts the movements of people to prevent the spread of a disease after an exposure or after becoming contagious.


This new virus has been named “SARS-CoV-2” and the disease it causes has been named “coronavirus disease 2019,” abbreviated to COVID-19.

Social distancing

Avoiding close contact with others. The two key components of social distancing includes limiting the number of people who gather together and making sure there’s enough space (recommended to be about six feet) between people.

Testing kit

The components used to test patients for illnesses, such as COVID-19.


A scenario where there are severe cases of COVID-19 and the flu at the same time. This situation could potentially overwhelm health systems and result in a shortage of hospital beds.


Viruses, such as SARS-CoV-2, are constantly changing over time. When they mutate, different variants of the virus emerge. There have been over 40 COVID-19 variants described to date and more will pop up around the world as time goes on. 


The branch of science that deals with the study of viruses.