Antibodies are large proteins created by certain types of blood cells in response to the presence of foreign substances (e.g. viruses) in the body. Once produced, antibodies bind to these foreign substances and either neutralize the threat directly or help other cells destroy it. Generally speaking, antibodies are specific to a particular foreign substance. For example, antibodies created in response to SARS-CoV-2 will look different from antibodies created in response to measles. If a person’s blood has a high enough concentration of antibodies specific to SARS-CoV-2, that person has likely developed long-term immunity to the disease. This is because once antibodies are formed for a particular disease, the immune system “remembers” the disease and can quickly produce those same antibodies if the person is ever exposed to that disease again.
Someone who is asymptomatic, also known as a carrier,is infected with COVID-19 but shows no symptoms (dry cough, fever, loss of sense of smell, sneezing, etc.) whatsoever throughout the duration of the infection. Although exact numbers are unknown, this is thought to be fairly common, more so than for many other illnesses. Estimates suggest that between 50 and 80 percent of those infected with COVID-19 may never show symptoms. This seems to be particularly common among children and young adults. It is not confirmed but suspected that asymptomatic carriers can still spread the disease.
Contagious refers to a person who is infected with a disease and is capable of spreading said disease through contact with other people. Contagious can also refer to a disease itself if that disease is capable of spreading from person to person. Lyme disease, for example, is caused by bacteria and is therefore an infectious disease. However, a person with lyme disease (and the disease itself) is not considered to be contagious, since lyme disease cannot spread from person to person. The novel coronavirus is both an infectious and a contagious disease, since it is caused by a virus and it can spread from person to person through contact. A person infectedwith the novel coronavirus is contagious/infectious.
Coronaviruses are a class of viruses that are named for the spikes on their surface that look like a crown. Coronaviruses are common and many cause only mild symptoms, like the common cold.
Covid-19 is the official name given by the World Health Organization for the disease caused by the novel coronavirus, SARS-CoV-2. It is short for “Coronavirus Disease 2019” because the first cases were identified in the year 2019.
A disease, broadly speaking, is a structural change or functional impairment of some part of the body due to a specific cause. Bacteria and viruses cause disease. For example, the novel coronavirus is a virus that causesthe disease COVID-19. Another example: Lyme disease is caused by the Borrelia bacterium.
ELISA (short for enzyme-linked immunosorbent assay) is a biochemical technique that is being used to determine whether a person was previously infected with the coronavirus, regardless of whether or not they had symptoms. The test works by recognizing the presence of antibodies (proteins the body creates in response to foreign substances) in an individual’s blood that are specific to SARS-CoV-2. The presence of these antibodies indicates that a person previously had the coronavirus. Researchers can use antibodies to study the disease and potentially develop immunological therapies. Though ELISA cannot detect an active infection, it has been useful in measuring how widespread the coronavirus has been in a particular population and identifying who is potentially immune to the disease.
Herd immunity is a form of indirect, communal protection from a disease that occurs when a sufficiently large number of individuals in the population become immune to the disease, either through vaccination or previous infection. These immune members of the population are incapable of spreading the disease and because viral infections like the coronavirus spread from person to person, having more immune individuals slows the spread. Herd immunity can protect members of the population who have not yet contracted a particular disease and are unable to be vaccinated, such as infants, the elderly, and those who are immunocompromised. The proportion of individuals who must be vaccinated in order for a population to achieve herd immunity varies by disease. For example, 19 out of 20 people must have the measles vaccine in order for herd immunity to prevent the spread in that population. A vaccine for COVID-19 does not exist yet, and therefore social distancing is the most effective way to prevent its spread.
A person is immune to a virus or bacteria if they possess antibodies (or better yet, T-cells which are cells made by the body to kill viruses and bacteria) that are specific to that virus or bacteria. When a person is immune, even if they are exposed again to a disease-causing virus or bacteria, their immune systems will destroy the invading virus/bacteria and they will neither become infected nor contagious. It is important to note that an asymptomatic person who is infected is not immune because they are still contagious and do not yet have antibodies and T-cells that are specific to that virus/bacteria.
The incidenceof a particula disease measures how many new cases of the disease occur in a population within a specified time period.
A person is infected when a virus or bacteria has entered their body.
A person is infectious if they are contagious, or easily capable of spreading the disease through contact with other people. Diseases can be also referred to as infectious, which simply means that they are caused by foreign substances (usually viruses and bacteria) invading the body.
After having had a disease and recovering from it, individuals have natural immunity, meaning their immune system has produced antibodies against the virus which usually prevent them from contracting the virus again.
PCR (short for polymerase chain reaction) is a DNA-based molecular biology technique that is being used in the most prevalent type of coronavirus test. After a sample is collected by inserting a sterile swab into the back of a person’s nose or mouth, a PCR test is used to analyze the sample and determine whether the person has the coronavirus. This test is only able to detect active infections and cannot detect past infections as it relies on the presence of the actual virus in the sample.
Someone who is pre-symptomatic has not yet developed symptoms but will eventually. After exposure to COVID-19, symptoms take an average of five to six days to appear and can take up to fourteen days. During this period, people can test positive for the virus but have not yet experienced any symptoms. While people are thought to be most contagious when their symptoms first appear, people who are presymptomatic can be contagious and spread the disease as well.
Prevalence refers to the total number of cases of a particular disease within a population in a given time period or at a given point in time.
SARS-CoV-2 is the official name of the novel coronavirus that causes the disease COVID-19. Note the similar name to SARS-CoV, which was the coronavirus responsible for the SARS outbreak between 2002 and 2004.
Sensitivity refers to the ability of a test to correctly identify true cases of a given disease. The sensitivity is a measure of the proportion of tests that return a positive result for individuals who truly have the disease, a “true positive.” Both sensitivity and specificity are important for measuring the efficacy of a test. Tests with high sensitivity and lower specificity would be likely to return a “false positive” result, meaning the test would indicate that the individual has the disease when they do not in fact have it.
Serology or serological are terms most commonly used to describe the study of blood serum (the liquid part of blood), which contains antibodies (see Antibodies), among other proteins. In the context of the coronavirus, serological testing is being used to determine whether a person has developed immunity to the novel coronavirus. ELISA is a common type of serological testing being used for this purpose.
Specificity refers to the ability of a test to correctly identify false cases of a given disease. The specificity is a measure of the proportion of tests that return a negative result for individuals who truly do not have the disease, a “true negative.” Both sensitivity and specificity are important for measuring the efficacy of a test. Tests with high specificity and low sensitivity would be likely to return a “false negative” result, meaning the test would indicate that the individual does not have the disease when they do in fact have it.
Someone who is symptomatic has some of the physical signs of COVID-19. These can range from very mild to very severe, but can include a fever, fatigue, chills, muscle pain, headache, sore throat, dry cough, loss of sense of smell or taste, and difficulty breathing. Symptoms typically take an average of five to six days to appear, although it can take up to fourteen days. The prevalence of COVID-19 symptoms is shown in the infographic below.
To be exposed to the coronavirus means you have either had direct contact with a person who is infected (i.e. you’ve been coughed on) or have had contact with a surface that an infected person has also contacted. Recent studies have found that the COVID-19 virus can survive up to three days on some surfaces. Individuals who have been exposed to the COVID-19 virus are at a higher risk of becoming infected.
Viral load is a measurement of virus particles. It is measured once a person has been infected and the virus has had time to replicate in their cells. It generally measures how many viral particles are in a unit of blood. Covid-19 patients with a higher viral load may experience more severe symptoms and may also shed more whole viruses.
Viral shedding, simply put, is a measure of contagiousness. Viruses operate by invading the body’s cells and hijacking their operations such that the body’s own cells are forced to create copies of the virus. Viral shedding refers to the release of the new virus cells from which were created.
Viral refers to anything related to or caused by a virus. Colloquially, it can be used to describe anything that spreads quickly.