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There are a variety of terms that are used in discussions of the novel coronavirus, SARS-CoV-2019, and COVID-19.

Airborne/aersolized transmission spread

Asymptomatic carrier

Breakthrough infections

Case fatality rate (CFR)

Close contact

Coronavirus

COVID-19

COVID-19 infection

Droplet transmission/spread

Endemic

Fully vaccinated

Hybrid immunity

Infection-to-fatality rate (IFR)

Infectious dose

Isolation

Long-haulers

Mild COVID-19

Multisystem inflammatory syndrome (MIS-C)

Mutations

Natural immunity

Post-acute sequelae COVID (P.A.S.C)

Post-vaccination infection

Presumptive positive

Positivity rate

Quarantine

RNA vaccine

SARS-CoV-2 or SARS-CoV-2019

Serologic test

Symptomatic case-fatality rate (sCFR)

Vaccine effectiveness

Vaccine efficacy

Viral load

V-safe after vaccination

Zoonotic


Airborne/aersolized transmission spread

There is a lot of controversy among scientists about this definition, hence the public health debate about how SARS-CoV-2, the virus that causes COVID-19 spreads. Generally, what is meant is spread of a contagious disease from a respiratory droplet that is small enough to float in the air or spread farther than 6 feet. The spread of these droplets may be affected by humidity, air flow, and temperature, but more research in this area needs to be conducted. While the World Health Organization still says the evidence isn’t clear is if these small droplets contain enough SARS-CoV-2 virus to cause someone else to become infected, a growing number of scientists [see this story: https://www.nytimes.com/2020/07/04/health/239-experts-with-one-big-claim-the-coronavirus-is-airborne.html] say the evidence is now clear that the virus is spread primarily through the air and should change its guidance accordingly.

Asymptomatic carrier

This is a healthy person who is infected by a pathogen and shows no symptoms of disease. People can become infected with a pathogen and experience no symptoms, but still transmit, or “carry” the pathogen to another person, infecting them. That person may then become sick, even if the original carrier does not. With COVID-19, it is hard to say just how many infectious people are asymptomatic. [researchers give an enormous range of 4% to 81% https://www.sciencealert.com/over-a-third-of-covid-infections-are-truly-asymptomatic-says-massive-new-analysis] More likely, many people are pre-symptomatic because people who are infectious may take several days before they show symptoms [such as headaches congestion and fatigue] and the symptoms are so varied between people that not everyone is aware that they have symptoms of COVID-19.

Breakthrough infections 

In vaccinology, a breakthrough infection means a person develops an infection from a pathogen after vaccination and may indicate the pathogen has become resistant to the vaccine. These types of infections are tracked in clinical trials to determine how well inoculation is working. In the case of COVID-19, the CDC defines breakthrough infection as someone who tests positive or develops an infection from SARS-CoV-2, the virus that causes COVID-19, two weeks or more after being fully vaccinated. However, using this term has caused confusion because not everyone who tests positive or develops an infection is contagious or seriously ill. For this reason, many health experts use the term post-vaccination infection instead of breakthrough.

Case fatality rate (CFR)

This is an estimate of the risk of mortality from a contagious disease. The CFR is calculated by dividing the number of deaths caused by a disease by the number of confirmed cases of that disease in each time period. The CFR is time and location-dependent and many factors can influence the rate such as, age and demographic characteristics, among others. For COVID-19, CFR estimates vary by country depending upon how many people have been tested, the number of those in the population older than 65, the strength of the health system and other factors. For example, in October 2021, the CFR from COVID-19 ranged from 7.6% in Mexico to 1.6% in the United States. [See https://coronavirus.jhu.edu/data/mortality]

Close contact

Close contact means being near a person (less than six feet) who has tested positive for COVID-19 in an environment with insufficient mitigation measures like social distancing, masks and ventilation for more than 15 minutes in a 24-hour period. Someone may also have been considered in close contact if the person has been hugged or kissed by someone with COVID-19, cared for someone at home sick with COVID-19, shared drinking or eating utensils with someone who tested positive for COVID-19 or has been coughed on or sneezed on by someone with COVID-19.

Coronavirus

Coronaviruses are a family of viruses, which cause respiratory illness in humans. It gets its name from the crown-like halo (or corona) surrounding the virus and can be seen under an electron microscope. Scientists have long identified coronaviruses circulating among animals such as camels, cats and bats. Still, only a few have jumped to people — a spread that is defined by epidemiologists as “zoonotic.”

Before 2020, six coronaviruses were known to be circulating among people, four of which cause about 25% of colds. Two others were known to cause extreme illness — severe acute respiratory syndrome (SARS) and Middle East Respiratory Syndrome (MERS). SARS and MERS spread between humans via respiratory droplets with close contacts, the way influenza and other respiratory pathogens have spread, but they don’t spread easily and could be controlled. Around 8000 people worldwide were infected with SARS and approximately 800 died; MERS infected 2500 and killed about 860. There has been no known community spread of SARS since 2003 and very little community spread of MERS. In January 2020, China announced the emergence of SARS-CoV-2019, the virus that causes COVID-19. The genetic sequence of the coronavirus causing COVID-19 shares some of the same genes as SARS. That is how SARS-CoV-2019 got its name. The “2019” designation was given because the virus is known to have begun circulating at some point late in 2019.

COVID-19

On February 11, 2020, the World Health Organization officially named the disease caused by the virus SARS-CoV-2, as COVID-19, a shortened name for coronavirus disease 2019. The “CO’ stands for coronavirus, “VI” stands for virus and “D” stands for disease. ‘19’ stands for 2019, the year that the virus was discovered to be causing illness in Wuhan, China. Coronaviruses are a kind of virus that looks, under an electron microscope, like it is surrounded by a halo, hence the name ‘coronavirus.’ The AP stylebook notes: “because COVID-19 is the name of the disease, not the virus, it is not accurate to write a virus called COVID-19.”

“Also incorrect are usages such as COVID-19 spreads through the air; scientists are investigating how long COVID-19 may remain on surfaces; she worries about catching COVID-19. In each of those, it should be the coronavirus, not COVID-19,” according to the stylebook.

COVID-19 infection

This term means that someone has a symptomatic disease [like cough, headache, fatigued see https://www.cdc.gov/coronavirus/2019-ncov/symptoms-testing/symptoms.html], named COVID-19. COVID-19 is caused by the virus SARS-CoV-2019, however not everyone who is infected with the virus gets sick. Some people who test positive for SARS-CoV-2019 do not develop a COVID-19 infection. Atlantic writer Katherine Wu notes to journalists to remember that COVID doesn’t infect people, but rather the virus does.

Droplet transmission/spread

A form of contagious disease spread that involves the spray of saliva or respiratory droplets, expelled when an infected person breathes, coughs, sneezes, talks or sings. If someone is nearby, they could breathe in these droplets and become infected. A person could also touch an item where the infected person’s droplets fell and then become infected when they touch their eyes or mouth. Most droplets are large enough that once they are expelled, they drop to the ground, within the range of about six feet. Therefore, public health officials ask people to keep six feet apart from others in public and to wash their hands.

Endemic

This refers to the constant presence of an infectious disease where cases are neither rising or falling in a geographic area.

Fully vaccinated

The term for receiving the full dosage of vaccine that scientists have determined is the amount needed to build the body’s immunity against a pathogen known to cause severe disease. That doesn’t mean someone is fully immunized, however. The body needs several weeks after vaccination to develop immunity. With COVID-19, the CDC counts someone as fully vaccinated the day a person gets the second dose of their Moderna or Pfizer vaccine and the day they get their first dose of Johnson & Johnson vaccine, but the CDC doesn’t consider someone fully vaccinated until two weeks afterwards. Since the CDC has just approved booster shots, the agency is now considering changing its definition of fully vaccinated. The definition ‘fully’ also causes confusion because vaccines never work 100% of the time. The vaccine’s effectiveness depends on a person’s immune system and whether a pathogen has evolved to escape defenses built by the vaccine.

Hybrid immunity

The term for someone who has developed infection from SARS-CoV-2 and received vaccination against the virus. Early research indicates that those that have had infection followed by vaccination may have longer protection against future COVID-19 illness , compared with those who have been vaccinated but never became infected with the virus. https://www.science.org/doi/10.1126/science.abj2258

Infection-to-fatality rate (IFR)

An epidemiology term that quantifies the chances that a person who contracts an infection from a pathogen will die from it. Not everyone who is infected by a pathogen will show symptoms of a disease. Not everyone who is infected by a pathogen will die. Knowing the IFR helps scientists determine the danger of a particular pathogen and develop countermeasures to prevent its transmission. With novel pathogens, like with the virus that causes COVID-19, this rate remains difficult to determine with precision because not everyone who is infected or sick is tested for infection.

Infectious dose

Infectious diseases spread when a healthy person encounters a pathogen expelled by someone sick, such as through a cough, sneeze, sexual activity or contact with fecal material. The amount of that pathogen necessary to make that healthy person sick is the infectious dose. With SARS-CoV-2, the virus that causes COVID-19, the infectious dose is unknown, but because no one has immunity to it, researchers suspect the dose is low.

Isolation

This policy involves separating people known or suspected to be infected with a contagious disease from those who are not sick to prevent them from transmitting disease to others. The definition of “suspected” is based on whether the person is showing symptoms of a contagious disease or whether they met certain laboratory criteria demonstrating they have likely been infected.

Long-hauler

A term for a person who is experiencing long-term health effects from COVID-19, the disease caused by the SARS-CoV-2 virus. While most people recover and return to normal health within days or a few weeks after infection, some people have symptoms that can last for months. Even those who weren’t hospitalized and seemed to initially have mild symptoms, can have symptoms that persist. The symptoms include shortness of breath, extreme fatigue and brain fog. Some even experience serious consequences like inflammation of the heart and loss of lung function. Because the disease is so new, public health officials and scientists are still studying why some infected individuals have symptoms that last longer than others.

Mild COVID-19

The CDC classified someone who has COVID-19 symptoms but isn’t sick enough to need hospitalization as having ‘mild’ COVID-19. However, there is an enormous range of illness from COVID-19. While some might just have a headache, another might be sick enough to need bedrest, or others develop persistent debilitating symptoms, called long-hauler COVID. Yet the CDC still defines these cases as ‘mild.’ Infectious disease specialists say it is more accurate to say that people can have mild, moderate to severe illness, but just not develop acute enough symptoms to need hospitalization.

Multisystem inflammatory syndrome (MIS-C)

This is a rare and potentially life-threatening inflammatory response associated with COVID-19, the respiratory disease caused by the SARS-Cov-2 virus. The syndrome affects mainly children and emerges weeks after they have contracted the virus.

Mutations

All viruses, including coronaviruses, replicate by attaching themselves to a living cell and subvert the cell’s DNA (the blueprint that directs its function) to reproduce the virus instead. As the virus copies itself, there are naturally errors or mutations. This is called antigenic drift and shift.

Natural immunity

This term refers to someone who has gotten sick and developed an immune defense against the disease-causing pathogen. Vaccines help a body develop the same immune defense without the risk of illness. The term is misused by those opposed to vaccines to suggest that a vaccine is causing someone to become ‘unnaturally’ immune to a disease, suggesting it is undesirable or dangerous. Immunologists suggest journalists use the words ‘infection-aquired’ immunity, rather than ‘natural’ immunity. Some immunologists have started using the word ‘hybrid-immunity’ referring to someone who has had SARS-CoV-2 infection and is vaccinated.

Post-acute sequelae COVID (P.A.S.C)

This is new terminology used by the CDC to describe long COVID, long-haul COVID or chronic COVID. Sequelae means the aftereffect of a disease. Post-acute sequelae COVID (P.A.S.C) represents a wide range of new, returning, and ongoing health problems that people experience for four or more weeks after being infected with SARS-CoV-2. Symptoms associated with post-acute sequelae COVID include shortness of breath or difficulty breathing, fatigue, brain fog, dizziness upon standing, chest pain, depression or anxiety, fever, loss of taste or smell and other multi-organ effects, including the heart, lungs, kidneys, skin and brain, and particularly the multisystem inflammatory syndrome in children. Though there remain many unknowns about the condition, scientists currently believe around 10% of those infected develop long-COVID symptoms.

Post-vaccination infection

No vaccine is 100% effective, as some people don’t mount an immune response and pathogens mutate to evade vaccines, but that doesn’t mean the vaccine didn’t work. Many public health officials suggest using the term post-vaccination infection instead of ‘breakthrough’ infection, to more precisely explain that some people may test positive to SARS-CoV-2 or develop an infection, but the vaccine was still effective.

Presumptive positive

This is a term used in the early days of the pandemic by the CDC related to the diagnostic testing process for a disease. A presumptive positive result is when a patient has tested positive by a state or local public health laboratory to infection by a pathogen but has yet to have been confirmed by the CDC. Public health laboratories are a network of specialized governmental health laboratories that operate at the state and local level across the country. Every state and the District of Columbia, has a public health lab and many states have local public labs in metropolitan areas and smaller communities. They are among the keys to public health surveillance and work closely with the CDC and other federal agencies, as well as international health agencies. The CDC has stopped using this phrase as state, local and federal health labs have sped up the process of confirming whether a person has tested positive for SARS-CoV-2.

Positivity rate

This refers to the percent of COVID-19 tests with positive results over a seven to 14-day period. As part of public health measures aimed at reducing the spread of COVID-19, the World Health Organization recommends that communities aim for a positivity rate of less than 5% for at least two weeks . A threshold of 5%Nor more is as an indication that the spread of SARS-CoV-2 is not under control in the community.

Quarantine

This involves health authorities separating and restricting the movement of people who have potentially been exposed to a contagious disease until it can be determined whether they have become sick or no longer pose a risk to others. Quarantines may take place in the home or other locations determined by health authorities. If a person shows no symptoms of the disease within the time when a person is considered contagious, they are considered disease-free and released from quarantine. With COVID-19, quarantine is meant to describe the amount of time someone who may have been exposed to SARS-CoV-2 is supposed to separate themselves from others until it is clear they haven’t developed the disease and aren’t contagious.

RNA vaccine

This is a class of vaccines that utilize a piece of genetic information from a specific pathogen to produce an immune response in the body and prevent disease.

SARS-CoV-2 or SARS-CoV-2019

On February, 11, 2020, the World Health Organization officially named the coronavirus causing illness, severe acute respiratory syndrome (SARS) 2, or SARS-CoV-2. The name was chosen because it is genetically related to another coronavirus that caused the SARS outbreak in China in 2002. The virus causes COVID-19 and was first discovered to be causing illness in 2019, hence why the virus is sometimes referred to by the name of "SARS-CoV-2019."

Serologic test

A blood test to detect the presence of antibodies against a microorganism. Antibodies are proteins that are part of the body’s overall immune response to fight a foreign presence, such as bacteria or a virus. A serologic test can determine whether a person has been exposed to a particular microorganism , and the potential that they are immune to a disease.

Symptomatic case-fatality rate (sCFR)

An epidemiology term that quantifies the risk that a person who is infected with a pathogen, and showing signs of illness, will die. Knowing this figure helps scientists determine the danger of a particular pathogen. The sCFR to SARS-CoV-2 continues to evolve because those with COVID-19 symptoms are the most likely to be tested. Estimates of the number of people infected with SARS-CoV-2 but don’t show symptoms average about 30 p%. That is why journalists may want to caveat the mortality rate figures with something to the effect of: "a mortality rate, based on the information that scientists have."

Vaccine effectiveness

Vaccine effectiveness means how well the vaccine performs in everyday life for a broad range of people. Data from effectiveness studies looks at the vaccine’s effects in a large, often diverse population, including those who are immune compromised and pregnant. With COVID-19, the term is widely misunderstood to mean efficacy, which is how well the SARS-CoV-2 vaccine performed in clinical trials. For example, in clinical trials, the Pfizer/BioNTech vaccine was found to have 95 % efficacy in preventing laboratory confirmed SARS-CoV-2 infection. However, in July 2021, data from Israel concluded the Pfizer vaccine effectiveness had fallen to 39% in preventing infection [https://www.cnbc.com/2021/07/23/delta-variant-pfizer-covid-vaccine-39percent-effective-in-israel-prevents-severe-illness.html], and the CDC recently approved vaccine booster shots for Pfizer, Modern and J&J vaccines.

Vaccine efficacy

Efficacy refers to how well a vaccine performs under ideal conditions. Efficacy can only be determined in clinical trials, and these trials typically have very specific criteria for participants. The criteria nearly always include age requirements and often have sex, gender, race or ethnicity requirements as well. Other potential criteria could relate to having or not having certain underlying conditions, having a certain severity of a particular disease, living in a particular geographical area, living in a rural or urban or suburban area or having public, private or no insurance, among other things. In clinical trials, the Pfizer/BioNTech vaccine was found to have 95 efficacy% in preventing laboratory confirmed SARS-CoV-2 infection. https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/Pfizer-BioNTech.html

Viral load

This is the measure of virus particles. Generally, it refers to the amount of virus present in the body once a person has become infected and the virus has replicated in the person’s cells. For most people, the higher the viral load, the worse the symptoms and outcomes.

V-safe after vaccination

The Centers for Disease Control and Prevention created V-safe, a smartphone-based tool that uses text messaging and web surveys to provide personalized health check-ins after people receive a COVID-19 vaccine. Through V-safe, the CDC is collecting data on any vaccine side effects and is also reminding people to get their second dose if one is needed.

Zoonotic

A zoonotic disease refers to a pathogen that has been living within an animal, and then, for an environmental or genetic reason, jumps into the human population where it can cause disease. Two of the best-known zoonotic diseases are influenza and the plague. The flu virus lives in the guts of waterfowl. The flu can spread to humans through a genetic shift that causes people to become ill. The plague is caused by the bacteria, Yersinia pestis. It can live inside fleas, which then bite humans and cause illness. In 1346, rats carrying fleas with Yersinia pestis traveled through trade routes in western Europe, causing a pandemic known as Black Death. Around 60% to 75% of all new diseases that affect humans are zoonotic in origin.