COVID-19 useful words and phrases

Clear definitions and explanations of some of the terms used to discuss COVID-19.

Health, disease and medical breakthroughs are topics of interest generally, but with so many people impacted by the COVID-19 pandemic, there are even more media stories on these topics than usual.

Even though many of these stories are written for the general public they often contain terms that are usually only used by health professionals and other types of researchers.

Some of these words used in these stories can be confusing, even if you’ve come across them before. To clear up some of this confusion we’ve created a list of COVID-19 useful words and phrases. 

We will be adding words to this glossary regularly. If there is a word that you would like to know more about email [email protected]



Word or phraseDefinition or explanation
AnosmiaLoss of your sense of smell. There are many reasons why this can happen including injury to the nerve that helps you smell, injury to the nose or sinuses, or a viral infection of the respiratory system. Anosmia is a reported symptom of COVID-19.
Antibodies Antibodies are:
  • small proteins that are produced by the immune system
  • also called immunoglobulins
  • produced by white blood (or plasma) cells.

Antibodies help defend the body against infectious organisms such as bacteria (eg, Escherichia coli, Staphylococcus aureus) and viruses (eg, influenza A virus, hepatitis C virus) that can cause disease.

There are different types of antibodies, some are produced soon after exposure to an antigen, while others appear after a longer period of time.

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To understand antibodies, it’s important to understand antigens. Antigens are substances that can trigger an immune response. They are usually an organism or particle that is foreign to the body, such as a bacteria, a virus or pollen. Blood or a transplant organ from another person can also act as an antigen.

If you have a normal immune response, your body will recognise a threatening antigen, like those attached to viruses, and will defend your body against it. A crucial part of this defence system is the production of antibodies, they tightly bind with a unique antigen, and either neutralise it or tag it for destruction.

The body makes thousands of antibodies and each one is assigned to a specific antigen. After the first encounter with an antigen, your body may take some time to produce the required antibody. But in the future, the memory cells of your immune system can recognise an antigen and swiftly produce antibodies in response. This is called ‘active’ or ‘acquired’ immunity, and it can occur after a disease or a vaccine.

Some people produce antibodies to substances that aren’t usually harmful, such as peanuts – this process is commonly known as an allergic response.

If a person has an autoimmune disease, they produce antibodies that stick to their body’s own proteins and damage healthy cells.

People who are immunodeficient cannot produce an appropriate immune response, which makes them prone to more serious bouts of illness.

Related: antibody tests, immunity, plasma, vaccines

Antibody tests

Blood tests that look for specific antibodies. Sometimes, they are called serology tests. Having the antibodies can be a sign you have been infected by (or immunised against) the disease caused by a particular antigen.

Tests that detect the presence of antibodies to the antigens that cause certain diseases, such as measles, can sometimes determine if a person is immune to that disease.

There are different types of antibody tests. Some are sensitive to the antibodies that your body produces immediately after an infection, while other antibody tests will detect antibodies that appear later.

Antibody tests are not recommended for diagnosing an active (acute) infection, because antibodies to an antigen take time to develop. You may be infectious even if your serology or antibody test results are ‘negative’.

Currently, a ‘reliable’ antibody test may show that someone has recovered, or is recovering, from COVID-19.

However not enough is known about COVID-19 for the presence of antibodies specific to SARS-CoV-2 to lead to any conclusions about immunity. In Australia, antibody tests for COVID-19 or any other disease cannot legally be advertised because their results are complicated and need to be interpreted by a health professional.

During an epidemic or pandemic like COVID-19, antibody tests show how many people in the population have or may have been infected with a disease.

Related: antibodies, immunity, plasma, serology, vaccines
Antiviral medicinesThese are medicines that stop a virus from infecting healthy cells or from multiplying. There are antiviral medicines available for:
  • different herpes viruses (that can cause cold sores, genital herpes and shingles)
  • the flu
  • COVID-19.

You can read more about COVID-19 medicines including antivirals here.

Related: coronavirus, virus

Bacteria Microscopic, single-celled organisms that can cause human diseases. Bacteria can be killed or damaged by antibiotics.

Bacteria are larger than viruses. Not all bacteria in our bodies cause disease. For example some bacteria in your digestive system can protect you from gut infections caused by other bacteria. 

Infections caused by bacteria tend to be in one area of the body (eg, tuberculosis is an infection in the lungs). Unlike a virus, a bacterium is a living organism and can reproduce without invading a host cell.

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COVID-19 is a viral infection, so antibiotics will not 'fight' the virus. Antibiotics might help if bacteria are able to cause infection because the person is already unwell, eg, pneumonia. 

Using antibiotics for infections that are not bacterial, or for infections that would go away without treatment, has led to a problem called antibiotic resistance. This means there are bacteria that cannot be treated with antibiotics. These bacteria are sometimes described as ‘superbugs’.

Related: coronavirus, virus

BoosterA booster dose is an extra dose of a vaccine after the first course of has been given. Booster doses are common for some vaccines given as part of the National Immunisation Program (NIP) Schedule, such as diphtheria, tetanus and pertussis (whooping cough). They are also part of the current COVID-19 vaccine program.
Cardiovascular system A group of organs that includes the heart (cardio) and blood vessels (vascular). The cardiovascular system is responsible for pumping and circulating blood around the body.

Cardiovascular diseases include diseases affecting the heart, such as heart failure and coronary artery disease, and disease affecting the blood vessels like a stroke.

Many COVID-19 symptoms affect the respiratory (lungs and airways) system. However, it can also cause problems with the heart and blood vessels. This is particularly true for people who already have problems with their heart, blood vessels or blood pressure.

Related: respiratory system, comorbidity

Cohort study

Research that involves studying a group of people (cohort) over a period of time to:

  • investigate the cause of a disease
  • make connections between risk factors and health outcomes.

During the COVID-19 pandemic, cohort studies have helped researchers learn about how the virus affects people, what health conditions are risk factors for severe illness and what actions help prevent the spread of the virus.

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This type of study is observational, which means that researchers are watching a group of people behave the way they normally would – there is no ‘experiment’ taking place. Typically, these researchers follow a group of people to learn more about a condition or to understand how certain risk factors might negatively impact on a person’s health in the long term.

Retrospective cohort studies use studies or information that already exists. They try to identify risk factors that might increase someone's chance of developing a specific health condition. For example, one retrospective-cohort study called 'Dying to be famous' looked at biographical data belonging to deceased rock and pop stars who reached fame between the years of 1956 and 2006, to see if negative childhood experiences predisposed them to risk-taking behaviour.

Prospective cohort studies look towards the future. Researchers may have a theory about what might cause a disease. To test this theory they observe a group of people – a cohort – over a period of time and see if there are any changes in health outcomes linked to possible risk factors they have identified.

The Framingham Farm Study is an example of a prospective cohort study, where 5209 men and women were recruited in 1948 and followed for decades to see if anything they did influenced their cardiovascular health. The study made several discoveries about the effects of smoking, cholesterol level and high blood pressure on heart health.

Related: epidemiologist, incidence, prevalence, randomised control trial


When a person has more than one health condition at the same time. For example someone who is diagnosed with COVID-19 might already have been living with multiple health conditions like asthma or high-blood pressure (hypertension). These conditions are comorbidities. They are sometimes called ‘existing’, ‘pre-existing’ or ‘underlying’ conditions’. 

Comorbid conditions can make a person more vulnerable to illness from other causes. During this COVID-19 pandemic, researchers have been paying attention to comorbidities to 1help protect people who are at higher risk of worse health outcomes.

Related: cardiovascular system, morbidity, respiratory system

Conjunctivitis A condition where the membrane (called the conjunctiva) that lines the inside surface of the eyelids and the front of the eyeball is inflamed. Conjunctivitis 
  • can be caused by infection (virus, or bacteria) or as part of an allergic reaction. 
  • is also known as ‘pink eye’ and is contagious if caused by a bacteria or virus.
  • is a reported symptom of COVID-19.
Note: ‘-itis’ at the end of a word usually signposts a disease characterised by inflammation. For example, appendicitis is a condition caused by the inflammation of the appendix. There are other ‘ itis’ examples in this document)
Contact tracing

A method to find people who have been exposed to a person with a confirmed case of an infectious disease, like COVID-19.

Close contacts of someone who has been exposed to infectious disease are at risk of being infected and infecting others. Close contacts will need to isolate.

Contact tracing has been around since before COVID. For example, it has been used to help identify people who may be at risk of Hepatitis C or HIV infection.

Related: quarantine, self-isolation


A large group of viruses that cause diseases in humans and animals. In humans coronaviruses can cause mild diseases like the common cold as well as more severe diseases such as COVID-19.

The coronavirus that causes COVID-19 is called SARS-CoV-2. Other illnesses caused by coronaviruses include Middle East Respiratory Syndrome (MERS) caused by the MERS coronavirus (MERS-CoV) and Severe Acute Respiratory Syndrome caused by the SARS coronavirus (SARS-CoV).

Corona means crown or wreath in Latin – under a microscope the coronavirus has bulbous spikes, like the pointy end of a crown.

Related: bacteria, COVID-19, pandemic, SARS-CoV-2


A new, infectious disease caused by the coronavirus SARS-CoV-2.

Viruses often have different names from the diseases that they cause, for example HIV is the virus that causes AIDS.

There have been a lot of words used to described COVID-19.

Before 11 February 2020, when the World Health Organisation (WHO) gave COVID-19 its name, the disease was often referred to as coronavirus in the media. However, there are many coronaviruses in the world, and only one type that leads to the disease COVID-19.

The name COVID-19 comes from Coronavirus disease 2019.

Related: coronavirus, epidemic, pandemic, SARS-CoV-2, WHO


A medical treatment that restores a sick person to health. If a person is cured, it means that they no longer have the condition that caused their illness. A cure is different from prevention, and from symptom management.

For example,. tuberculosis can be cured by taking certain medicines while measles can be prevented with a vaccine. Generally, chronic conditions cannot be cured but their symptoms can be treated. Diabetes, for example, can be managed with medicines such as insulin injections.

There is currently no cure for COVID-19. There are medicines that can help treat symptoms, and vaccines that can make it less likely you will get sick if infected.

Related: treatment, vaccine


Changes to, or loss of, the sense of taste. There are a number of reasons why this can happen including as a side effect of certain medicines (eg, chemotherapy), and as a result of viral infection.

This can be a symptom of COVID-19.


An illness, or other health-related event, that affects a large number of people in a community, population or region, and is occurring at a higher rate than expected. An epidemic can be caused by a disease (eg, typhoid, SARS-CoV-2), or by health-related behaviours (eg, no clean water, poor hygiene).

A pandemic is declared when the infectious disease outbreak occurs on a global level.

Related: contact tracing, COVID-19, epidemiologist, pandemic


Public health professionals and researchers who study patterns, causes and prevention of disease and injury in people. During an outbreak, like COVID-19, they study: 

  • the affected population to identify the agent responsible
  • the people who are at risk
  • how to stop the spread of the disease
  • data to work out how to stop a similar outbreak from happening again.

Related: cohort study, contact tracing, incidence, prevalence, randomised control trial, WHO



Word or phraseDefinition or explanation
Herd immunity This is a type of infection control that occurs naturally, or through immunisation programs. It happens when a large enough portion of a population becomes immune to a disease to stop further spread. Immunity may be either by recovering from the disease or by being vaccinated against it.

In the case of COVID-19, the possibility of herd immunity remains unclear due to the uncertainty of long term immunity to this virus.

Related: antibodies, immunity, plasma, vaccine

Hygiene Actions that prevent the spread of disease and maintain health through cleanliness.

Most infections enter our bodies when we touch our face with unwashed hands.

While we don’t have a cure for COVID-19, we can prevent the spread of germs by washing hands regularly, and covering your mouth while coughing or sneezing. Discarding items like tissues shortly after use is also a way of practicing hygiene. Using a face mask in certain situations can also help reduce spread

Related: physical distancing, quarantine, self-isolation

Immunity Immunity is the ability to resist illness when exposed to a disease.

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There are several ways to develop immunity.

Active immunity is the result of being exposed to a disease, or vaccine for a disease. The exposure prompts your immune system to produce antibodies that help your body resist infection.

If you re-encounter the disease your immune system’s ‘memory cells’ will swiftly reproduce those antibodies which should protect you from that disease.

Passive immunity occurs when a person receives antibodies belonging to another person (see plasma) ,or naturally when an infant absorbs their mother’s antibodies from the placenta or via breast milk.

This type of immunity does not last for a long time, because the persons own immune system was never activated and so their body did not produce it’s own protective antibodies.

Related: antibodies, antibody tests, herd immunity, plasma, vaccine

Incidence This term is used to describe the rate of new illness or injuries (morbidities) within a precise population over a specified period of time. Incidence can mean the number of new cases in a community, or the number of new cases in a unit of population over a period of time.

Related: morbidity, mortality, prevalence

Kawasaki disease

A rare inflammatory condition that mostly affects children under 5 years of age. We don’t know what causes Kawasaki disease.

We do know that it’s not contagious and that in Australia, there are around 200–300 cases of Kawasaki disease recorded every year.

Kawasaki disease existed before the COVID-19 pandemic but has received attention because of a similar syndrome called ‘multisystem inflammatory disorder in children and adolescents.’

Cases of multisystem inflammatory disorder in children and adolescents have been recorded in UK, Europe and North America.

Children with symptoms of the disorder have either been in contact with someone who has had COVID-19, or have antibodies to SARS-CoV-2 in their blood – implying that they have been infected with the coronavirus in the past.

Little is known about multisystem inflammatory disorder in children and adolescents but the World Health Organization is monitoring recorded cases of the condition.

Related: morbidity, epidemiologist, World Health Organization



Word or phraseDefinition or explanation
Morbidity Another word for illness. It refers to any physical or mental health symptom or condition that makes someone feel worse than usual.

The ‘rate of morbidity’ or ‘morbidity rate’ can also be used to discuss the amount of disease within a defined population over a specified period of time, but this is usually expressed with terms like ‘incidence’ and ‘prevalence’.

If you have more than one condition at a time then you may be described as having co-morbidities.

Related: epidemic, epidemiologist, comorbidity, incidence, prevalence, mortality, mortality rate


Another word for death, often used by researchers and statisticians to describe the rate and pattern of death within a specific population, during a specified time period.

For example, the Australian Bureau of Statistics’ wrote: “Reductions in mortality over the past 50 years have seen life expectancy at birth increase by more than 10 years…” in their ‘Changing Patterns of Mortality in Australia’ report.

Related: epidemiologist, mortality rate

Mortality rate

The rate of deaths recorded within a specific population during a defined time period.

There are several different measurements of death that researchers are interested in looking at during a health event such as the COVID-19 pandemic.

Related: incidence, prevalence


Muscle pain. This can be a symptom of COVID-19.

Note: ‘algia’ in a word is usually an indicator that the word refers to a type of pain. For example, neuralgia is pain due to a damaged or irritated nerve.

MyocarditisThis is inflammation of the heart muscle. The inflammation can affect how it pumps. Myocarditis is usually caused by a viral infection.

Myocarditis is a rare side effect of some COVID-19 vaccines. It is temporary in most cases, and goes away after rest and treatment.


A worldwide outbreak of a disease. The World Health Organization (WHO) is responsible for declaring pandemics because it has access to global public health data.

Pandemics often start as epidemics that have been confined to a community or region. For example, AIDS was considered an epidemic in West Africa for several decades before becoming a pandemic in the late 20th century.

On 11 March 2020, WHO announced that COVID-19 was a pandemic.

Related: epidemic, WHO

Peer review The process where relevant experts (‘peers’) evaluate the quality of other experts' work before publication, to ensure that the methodology and findings are rigorous and coherent and relate to prior knowledge of the topic by referencing past research. 

The pressure of publishing during a pandemic has led to a rushed peer-review process for research relating to COVID-19 and as a result, some early studies have come under question.

Related: epidemiologist, cohort study, randomised control trial

PericarditisThis is swelling of the lining around the heart. The swelling can cause sharp pain in the chest. Pericarditis is usually caused by a viral infection.

It is a rare side effect of some COVID-19 vaccines. It is temporary in most cases, and goes away after rest. Some cases may need treatment.

Physical distancing

This is a type of infection control that involves staying physically distant from other people to prevent the spread of disease. In Australia, the Department of Health and Aged Care recommends staying 1.5 metres from other people where possible during the COVID-19 pandemic.

Sometimes the term ‘social distancing’ is used instead of ‘physical distancing’ but the World Health Organization stopped using the term ‘social distancing’ because it wants people to remain connected.

Related: quarantine, self-isolation


The liquid component of blood. It’s made up mostly of water and contains electrolytes and crucial proteins, including antibodies.

Plasma collected from people who have recovered from a disease is called convalescent plasma. People who have recovered from COVID-19 have been urged to donate their plasma for research, because it’s rich in antibodies and may be a potential treatment for COVID-19.

The idea behind this therapy is that it may provide people who are infected with COVID-19 with antibodies, before they produce their own. This is an example of passive immunity.

Related: antibodies, treatment, immunity, serology


This term is used to described the number of people who have a medical condition or risk factor, during a defined time period. Prevalence describes how common something is for a particular population for a specified period of time.

For example if we were looking at the number of COVID-19 cases in Australia, we could say that between 3 January 2020 and 31 August 2023 the prevalence was 10,018,025 confirmed cases of COVID-19.

Related: cohort study, comorbidity, epidemiologist, incidence, morbidity


A type of infection control using isolation to stop the spread of a disease. For example, animals are quarantined for 3 months in the case of rabies. Quarantine has been a key method of stopping infection spread during the COVID-19 pandemic.

In Australia, people who are in quarantine should not leave their place of residence unless it’s an emergency. If they develop symptoms, they are advised to be tested for COVID-19.

Related: contact tracing, hygiene, physical distancing, self-isolation



Word or phraseDefinition or explanation
Randomised controlled trial

The type of study considered to be the ‘gold standard’ (highest quality) in testing the effect of a treatment.

Trial participants are randomly divided into two or more groups. One group does not receive the treatment. This is the control group. All other groups will be given the treatment that is on trial.

Sometimes, the group that is not receiving treatment will be given a placebo. A placebo is a substance, test or procedure that looks the same as the new treatment, or is delivered the same way, but contains inactive ingredients. Using a placebo is a way of making sure that any improvements or benefits are in response to the actual treatment being tested, not to the idea of the treatment.

The results from both groups are eventually compared to see if receiving the proposed treatment has better health outcomes than not receiving the treatment.

Read more about clinical trials

Related: cohort study, cure, epidemiologist, treatment

Respiratory system

The group of organs that make breathing (respiration) possible. This includes the lungs, mouth, nose, diaphragm and airways.

COVID-19 is a respiratory disease, although it can cause cardiovascular complications – especially for those with pre-existing heart conditions or uncontrolled, high blood pressure.

Related: cardiovascular system, COVID-19


The shortened name of the virus that causes the disease called COVID-19. The International Committee on Taxonomy of Viruses (ICTV) gave SARS-CoV-2 its name. The World Health Organization (WHO) named the disease COVID-19.

Virus names are based on their genetic structures, which helps researchers target vaccines and medicines appropriately.

On 11 February 2020 ICTV assigned the name ‘severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)’ to the virus that causes COVID-19.

Related: coronavirus, COVID-19, virus, WHO


This is a type of infection control where a person diagnosed with, or suspected of having, an infectious disease avoids contact with other people.

A person (outside of hospital) who is told to self-isolate can only leave their house or other place of residence if they need urgent medical care. They are advised to physically distance themselves from anyone who lives with them, and to avoid contact with people who don’t (outside of an emergency scenario).

Related: contact tracing, hygiene, quarantine


A medical science that studies blood serum, a fluid derived from plasma which is rich in antibodies. Serology tests look for antibodies in your blood to see if you have been vaccinated against or have had a specific disease in the past. The presence of some antibodies can also indicate an allergy or an autoimmune disease.

Note: a word that ends in ‘-logy’ usually indicates that the whole word relates to a type of science or theory. For example, biology is a branch of science that studies living organisms.

Related: antibodies, antibody tests, immunity, plasma, vaccine


A medicine, or other health-related intervention, that will reduce the symptoms of a disease or eliminate the disease completely.

Chemotherapy, for example, is a treatment for cancer. It can cure specific types of cancer by destroying cancer cells and can also be used to improve the symptoms of cancer, when a cure is not possible.

Treatments are important for chronic disease, which cannot be cured. For example, there are medicines that can help people with asthma breathe more easily, but they will not cure asthma.

Related: cure, randomised control trial

Underlying conditionSee comorbidity

Medicines that help prepare our immune systems to defend against infection from certain diseases. Usually vaccines are given before the person is exposed to the disease. Each vaccine stimulates the immune system to make antibodies against a particular virus or bacteria. Some vaccines are given as injections, others are swallowed.

Some vaccines provide lifelong immunity but others may require ‘booster shots’ to maintain immunity.

The process of receiving a vaccine is called a vaccination, which is sometimes called an immunisation, but being vaccinated is different to being immunised. You are only immunised against the disease when your body starts producing antibodies.

There are a number of vaccines approved for use. 

Read more about vaccines and COVID-19

Related: antibodies, antibody testing, immunity, plasma, treatment, serology


An agent that causes disease. Viruses are significantly smaller than bacteria but they can be just as dangerous to your health. Different viruses cause diseases such as influenza, smallpox, measles, chickenpox and shingles.

A virus is only active when it enters a host cell in an organism (such as a human body). A virus can only be harmful to an organism once it enters a living cells and starts to multiply.

Because of the way viruses reproduce, they tend to spread throughout the whole body – rather than staying in one region like bacteria do. 

Viruses are also capable of invading the cells of bacteria.

Antibiotics cannot destroy a virus.

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

Related: bacteria, coronavirus, COVID-19, SARS-CoV-2

The World Health Organization (WHO) was founded in 1948, with the objective of helping countries achieve better health for their citizens through research, funding, public health campaigns and many other projects and programs.

The WHO defines health as ‘…a state of complete physical, mental and social well-being’, not just the absence of illness.

One of its many roles is to direct and coordinate international health work. During health-related emergencies, such as a global pandemic, the WHO must provide technical assistance and ‘…necessary aid upon the request or acceptance of Governments.’

194 countries are member states of WHO.

On 11 March 2020 the WHO announced that COVID-19 infection had become a pandemic. The group continues to monitor the situation around the world, collect information, support research and provide guidance for how to manage this infection.

Related: epidemic, pandemic