From Pandemic to Social Distancing: A Coronavirus Glossary

    A woman wears a face mask, to protect against the coronavirus, outside of the United Nations in Manhattan on March 10, 2020. The World Health Organization declared the coronavirus outbreak a global pandemic after it spread across six continents and more than 100 countries and as the virus spread, new terms are entering the lexicon.

    Jenny Gross and Mariel Padilla (The New York Times)

    When is an epidemic considered a pandemic, and what is the difference? What do health officials mean when they recommend “self-quarantining” or “social distancing”?

    As the coronavirus spreads around the world, new terms are entering the lexicon and we’re here to help. Here’s a guide to the words and phrases you need to know to keep informed of the latest developments.


    On March 11, the World Health Organization declared the coronavirus outbreak a pandemic after it spread across six continents and more than 100 countries. A pandemic is the worldwide spread of a new disease that affects large numbers of people. The WHO had avoided using the word because it didn’t want to give the impression that the disease was unstoppable.


    An epidemic is a regional outbreak of an illness that spreads unexpectedly, according to WHO. The U.S. Centers for Disease Control and Prevention defines it as an increase, often sudden, in the number of cases of a disease above normal expectations in a set population.


    The technical name for the coronavirus is SARS-CoV-2. The respiratory disease it causes has been named the “coronavirus disease 2019,” or COVID-19.

    Coronaviruses are named for the crown-like spikes that protrude from their surfaces, resembling the sun’s corona. Coronaviruses are among a large number of viruses that are common in people and many animals.

    While antibiotics don’t work against viruses, researchers are testing drugs that could disrupt viral proteins and stop the infection.

    State of Emergency

    A state of emergency can be declared during natural disasters, epidemics and other public health emergencies. Declaring a state of emergency gives government officials the authority to take extra measures to protect the public, such as suspending regulations or reallocating funds to mitigate the spread of a disease.


    The incubation period is the time it takes for symptoms to appear after a person is infected. This time can be critical for prevention and control, and it allows health officials to quarantine or observe people who may have been exposed to the virus.

    The new coronavirus has an incubation period of two to 14 days, according to the CDC, with symptoms appearing about five days after infection in most cases.

    During the incubation period, people may shed infectious virus particles before they exhibit symptoms, making it almost impossible to identify and isolate people who have the virus.

    Social Distancing

    The virus can easily spread in dense places in a packed subway car, for example, or at a rally or concert.

    Social distancing refers to measures that are taken to increase the physical space between people to slow the spread of the virus. Examples include working from home, school closures and the postponement or cancellation of mass gatherings.

    By maintaining a distance of 6 feet from others when possible, people may limit the spread of the virus.


    This is key to keeping the virus from spreading, along with measures like social distancing, frequent hand-washing and wearing masks.

    While isolation refers to separating sick people from people who aren’t sick, quarantine refers to the separation and restriction of movement of people who were exposed to the virus to see if they become sick.

    If you’ve left an area with widespread or continuing transmission, including China, Iran, Italy and South Korea, you should self-quarantine at home for a period of 14 days from the time you left, according to the CDC.

    While in quarantine, you shouldn’t receive any visitors and must stay 3 to 6 feet from others at all times.

    According to the CDC, once someone has been in isolation for 14 days and hasn’t become ill, he or she is not considered to be a risk to other people.

    Fatality Rate

    The case fatality rate is the number of deaths divided by the total number of confirmed cases. Eventually, scientists hope to have a more comprehensive number called the infection fatality rate, which includes everyone who was infected with the virus.

    The WHO estimates the fatality rate of the new coronavirus to be about 3 percent, based on current data, but experts suggest 1 percent is more realistic.


    The R-naught, or R0, is a virus’s basic reproductive number an epidemiologic metric used to describe the contagiousness of infectious agents.

    At its simplest, the basic reproductive number can show us how worried we should be about infection, according to Dr. Adam Kucharski, a mathematician at the London School of Hygiene and Tropical Medicine. If the R0 is above one, each case is expected to infect at least one other person on average, and the virus is likely to keep spreading. If it’s less than one, a group of infected people are less likely to spread the infection.

    Research is still in its early stages, but some estimates suggest that each person with the new coronavirus could infect between two and four people.


    The virus’s high transmission rate has made it difficult to effectively contain the outbreak. Containment refers to the use of any available tools to mitigate the spread of a disease, said Adam Ratner, the director of the division of pediatric infectious diseases at NYU Langone Health.

    Ratner said the coronavirus is particularly hard to contain because it is “reasonably transmissible” and some people who don’t have a lot of symptoms can still pass the virus to others. “That’s been part of the problem,” he said, “but it also points to the fact to how interconnected we all are and how quickly this thing spread from Asia to the rest of the world.”

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