COVID-19 Glossary

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In epidemiology, an R0 is a measure of transmission. It basically represents the average number of people that one infected person will, in turn, infect. Based on current information, coronavirus has an R0 somewhere between 2 and 3, so the average infected person will pass the virus on to two or three more people. That makes it more contagious than the flu, which has an R0 of about 1.5. Measles, one of the most contagious viruses, has an R0 of about 15.

R0 / reproductive rate

An epidemiological metric used to describe the contagiousness or transmissibility of infectious agents, which is usually estimated with complex mathematical models developed using various sets of assumptions. It is an estimate of the average number of new cases of a disease that each case generates, at a given point in time. 


An antiviral that may work against coronavirus. It is currently in clinical trials but for bureaucratic and scientific reasons those trials may not be considered valid in the U.S.

respiratory illness

A disease that impacts lungs, throat and airways. Respiratory illnesses primarily cause coughing, fever and can lead to severe pneumonia. Most are spread in respiratory droplets, which are virus-filled drops of water we shoot out when we cough and sneeze. Although respiratory illnesses attack airways, they can ultimately damage a number of other organs.

respiratory system

The entire system that lets you breathe. Not just your lungs, but your nose, your airways, your trachea, your mouth and your diaphragm are all a part of the respiratory system.


Ribonucleic acid; a type of genetic material. Humans, plants, animals, bacteria and some viruses have both DNA and RNA. In humans, DNA stores the information that says how to code our body, while RNA reads that DNA and helps make the proteins and enzymes that make things happen. Sometimes, the RNA can make things happen on its own, too. Coronavirus is an RNA virus or ribovirus, which means that drugs that treat it need to somehow block the virus’ RNA from invading our cells.


A way to sequence DNA and RNA in near real time. Most tests for coronavirus are RT-PCR tests. These tests have a high rate of false negatives but a low rate of false positives, so most people are tested twice.