What is COVID-19?

The research community races to address a mysterious new disease that threatens lives, livelihoods, and institutions around the world. Every day scientists make discoveries about where the novel coronavirus came from, how it spreads, and how it affects its victims differently. Developing effective and scalable means for testing, treating, and vaccinating against the virus all present mind-boggling challenges.

Search below to discover key terms and definitions related to COVID-19 and coronavirus research.

Terms and definitions

Antibody Testing

An antibody test, also known as a serology test, is done with a blood sample that may identify past infection of the virus that causes COVID-19. An antibody test looks for evidence of the body's immune response to the virus. While antibody tests blood after infection, with COVID-19, it's still not fully known what the presence of its antibodies means.

Contact Tracing

Contact tracing is used to help prevent the spread of infectious diseases. Generally, contract tracing identifies people who have an infectious disease (cases) and their close contacts (other people who may have been exposed) in an attempt to interrupt disease transmission. For COVID-19, this includes asking both the cases and the contacts to voluntarily quarantine themselves.

Convalescent Plasma

Convalescent plasma is the collection of blood plasma from someone who has recovered from COVID-19. Plasma is transfused into someone infected with the virus in the hopes antibodies from the recovered person can help the patient who is sick.


When SARS CoV-2 virus infects humans and causes disease, it is called COVID-19. COVID is short for "coronavirus disease." The number "19" refers to the fact that the disease was first detected in 2019, though the pandemic started in 2020.

Diagnostic Testing

The COVID-19 diagnostic test that uses a nasal swab is known as the molecular PCR test. This test collects samples of cells and fluids from a patient's respiratory system, which enables the identification of specific genes for the SARS-CoV-2 virus that causes COVID-19.

Droplet versus Airborne Transmission

Airborne transmission is distinct from droplet transmission in that 'airborne' requires an infectious pathogen to remain viable in the air for extended periods of time and able to infect people at distances greater than 1 meter. The evidence is not yet clear if SARS CoV-2 can easily become aerosolized or truly 'airborne' and transmitted over long distances and time. Currently, SARS CoV-2 is primarily spread through direct contact and short distances by respiratory droplets when an infected person coughs or sneezes. The respiratory droplets land in the nose or mouth of people who are near the infected individual.

Emerging Infectious Disease

An infectious disease emerging in human populations for the first time.

Flatten the Curve

"Flattening the curve" refers to slowing down the rate of new COVID-19 infections as to not overwhelm healthcare systems with an influx of cases at a given time while maintaining the necessary resources to care for sick patients. The 1918 Spanish flu Pandemic exemplifies how interventions such as social distancing, restricted travel, and improved handwashing hygiene help to reduce the number of cases at a given time. "Flattening the curve" is a result of early non-clinical interventions to support the healthcare system capacity.

Herd Immunity

Herd immunity is indirect protection from having a large percentage of a population immune to an infectious disease. Herd immunity not only shields vulnerable individuals from infection, but it can also slow the spread of disease.


A previously unknown or undetected pathogen in an ecosystem.

One Health

One Health is an approach that recognizes the close connection between people's health and the health of animals and our shared environment. One Health is recognized in the United States and globally as an effective way to address complex health issues at the human-animal-environment interface, including zoonotic diseases.


Wearing personal protective equipment (or PPE) is a crucial step to both stopping the spread of infection and keeping healthcare workers safe. PPE items include wearing a face mask, gloves, face shields, gowns, or Tyvek suits worn to minimize exposure to hazards and infections.


A Pathogen is defined as a bacterium, virus, or another microorganism (e.g. fungus) that can cause disease.

Reverse Zoonosis

Reverse Zoonosis occurs when a human transmits a pathogen to the animal.


Severe Acute Respiratory Syndrome, the disease caused by the SARS-CoV-1 coronavirus that emerged in China in 2002 and also causes serious respiratory disease in humans. SARS-CoV-1 and SARS-CoV-2 viruses are closely related.


SARS-CoV-2 is the name of the coronavirus that causes the disease COVID-19.


When a pathogen (e.g. virus) naturally present in a host successfully moves into another host species (cross-species transmission) it "spills over."


Different genetic variations of a virus are referred to as strains.

Viral Host or Host Species

A viral host is an organism that harbors a pathogenic (disease-causing) virus. Some viruses can be "hosted" by more than one species.

Viral Mutation

Random viral mutation can help track the spread of a pathogen and learn about its transmission routes and dynamics. As the pathogen replicates and spreads, its genome needs to be replicated many times and random mutations (copying mistakes) will accumulate in the genome; this is normal.

Zoonotic Diseases

Zoonotic diseases are illnesses that can spread between animals and people. Examples of zoonotic diseases include Rabies, West Nile Virus, COVID-19, Lyme Disease, and Plague.