Active immunity

The body’s creation of antibodies that help protect the immune system against a certain disease. Active immunity to a disease can happen in two ways, either by getting the disease or through getting a vaccine that prevents that illness.

Adverse event

Any health problem that happens after a shot or other vaccine. An adverse event might be truly caused by a vaccine, or it might be pure coincidence and be caused by something else. An adverse event may be mild, moderate, or serious.

There are different types of adverse events:

  • True reactions to the vaccine, such as side effects and allergic reactions.
    • Side Effect- Any health problem shown by studies to be caused by a vaccine. Like any medication, vaccines can cause side effects. Usually vaccine side effects are minor (for example, a sore arm where a shot was given or a low-grade fever after a vaccine) and go away on their own within a few days.
    • Allergic reaction -A response by the body that occurs in some people when the immune system overreacts to a harmless substance known as an allergen.
  • Unrelated health problems.
    These are experiences that would have occurred even if the person had not been vaccinated. They happen after vaccination but are not caused by the vaccine.
  • Health problems that cannot be related directly to the vaccine.
    The cause of these events is unknown, and there is not enough evidence to say whether they are caused by a vaccine.



Small liquid or solid particles that are suspended in a mist or gas, usually the air.

Aerosol transmission (or airborne transmission)

The spread of a disease through the air through tiny aerosol particles. COVID-19 aerosol particles get breathed out in a fine mist when an infected person talks or breathes, and they may be breathed in by other people.

Allergic reaction

A response by the body that occurs in some people when the immune system overreacts to a harmless substance known as an allergen.  Allergens may be pollen, certain foods, latex, mold, insect stings, eggs, or certain vaccine ingredients. There may be many symptoms of an allergic reaction ranging from mild to serious, such as itchy eyes or nose, swelling, rash, trouble breathing,  or, in some cases, anaphylaxis.


An immediate and severe allergic reaction to a substance, such as food or a vaccine. Symptoms of anaphylaxis include breathing trouble, loss of consciousness and a drop in blood pressure. This condition can be deadly and needs immediate medical attention.


A substance that kills or slows the growth of bacteria and is often used to treat infection. Antibiotics will not prevent or treat viruses such as COVID-19.


A protein made by the immune system to protect the body from foreign substances from outside of the body, such as viruses or bacteria. Antibodies protect the body from disease by attaching to the substance (such as COVID-19 viruses) and destroying them, which stops them from infecting the body’s cells.


Not showing any symptoms or signs of disease or illness. Some people without any symptoms can still have and spread COVID-19.

Clinical trial

A research study in which volunteers receive a new vaccine or other treatments so that scientists can evaluate how well it works. In addition to taking the drugs or treatments being tested, participants may help measure results by reporting on how they feel and by allowing healthcare providers to conduct follow-up exams that might include blood tests or other testing.

Clinical trials are carefully designed, reviewed, and completed. The principal investigator is the person in charge of the trial. He or she is a scientist who is an expert in what the trial is about. The principal investigator takes the lead in designing a clinical trial, choosing the research team, and carrying out the study. Other scientists called investigators are part of the research team.

Before a drug is tested in a clinical trial, considerable research is done in a laboratory in developing the drug and testing whether it can protect against the virus or not.

Clinical trials typically take place in three stages.

Vaccine Development

Phase 1 trials usually involve a few dozen people and are designed to observe whether a vaccine or drug is safe. Scientists give the vaccine to a small number of people (often 15 to 30) to confirm that it works to make the immune system become active to address the virus. Phase 1 trials aim to find the best dose of the drug or vaccine with the fewest side effects and to determine if the vaccine is safe enough to continue testing.

Phase 2 trials, involving hundreds of people, allow researchers to try out different doses and gather more measurements about the vaccine’s effects on the immune system. Scientists give the vaccine to hundreds of people split into groups, such as children and the elderly, to see if the vaccine acts differently in them. These trials further test the vaccine’s safety.

Phase 3 trials, involving thousands or tens of thousands of volunteers, determine the safety and efficacy of the vaccine or drug by waiting to see how many people are protected from the disease it is designed to fight. Scientists give the vaccine to thousands of people and wait to see how many become infected, compared with volunteers who received a placebo (a substance that does not contain the vaccine). These trials are randomized, which means they are put into trial arms (either receiving vaccine or placebo) by chance. Randomization makes sure that the people in the trial arms (groups) are alike, so that scientists know that the results of the trial are due to the vaccine and not due to differences between the people in the trial arms. These trials can determine if the vaccine protects against the coronavirus, measuring what’s known as the efficacy rate. Phase 3 trials are also large enough to reveal evidence of relatively rare side effects.

The data from clinical trails are generally published in medical journals after “peer-review” i.e., other experts. In  general, when an article goes through peer review provides more confidence in the integrity of the study and the data. It is therefore important that there is complete transparency about data from clinical trials to ensure confidence in the vaccine or any drug for that matter.

For more information on this topic, visit the New York Times

Community spread (also called community transmission)

The spread of an illness within a particular location, such as a community, neighborhood, or town. Within community spread, there is no clear source of the infection (such as a history of travel or connection to a known case).


A family of viruses that mostly cause respiratory illnesses. Coronaviruses cause COVID-19, SARS (Severe Acute Respiratory Syndrome), and MERS (Middle East respiratory syndrome), among other illnesses. They get their names from the crown-like spikes (coronas) that appear on the virus under a microscope.


The name of the illness caused by the coronavirus SARS-CoV-2. COVID-19 stands for “coronavirus disease 2019.”


The characteristics of a population. These may include the percentage of the population of different ages, sexes, race/ethnicities, education, employment, residence, and geographic location.


A small drop of liquid, such as those of mucus or saliva that are expelled (sprayed out) into the air when a person coughs or sneezes.

Droplet transmission

The spread of a disease such as COVID-19 by the spread of droplets. Droplets are expelled when an infected person coughs, talks, or sneezes. Transmission occurs when these droplets land in the nose, throat, or eyes of another person.

Foreign substance

A substance that comes from outside of the body, such as a virus or bacteria. A foreign substance in the body’s tissues may be recognized by the immune system, resulting in an immune response that causes the body to defend itself against the substance.

Herd immunity (also called community immunity)

A situation that occurs when a large enough number of a population is immune to an infectious disease (either through already having had the disease or through vaccination) to limit or stop the spread from person to person in that area, even among those who do not already have immunity.

Immune system

The immune system protects the body from infections, viruses and diseases. It is a network of cells that forms a system in the body responsible for fighting disease. Its primary role is to identify foreign substances in the body (bacteria, viruses, fungi or parasites) and develop a defense against them. If the substance enters the body again at a later time, the immune system can remember and repeat this response.


Protection against a disease.


The process of being made immune or resistant to an infectious disease, typically through receiving a vaccine.

Immune response

The response made by the immune system to defend itself against a disease or pathogen. The immune response is first created when the body encounters either the disease or a vaccine, and then it is repeated if the disease attempts to enter the body at a later time.

Incubation period

The time it takes for someone with an infection to start showing symptoms of an illness.


The process of separating people who are sick with a contagious disease such as COVID-19 from people who are not sick.

mRNA vaccines (also called messenger RNA vaccines)

mRNA vaccines that contain harmless sections of protein from the virus that causes COVID-19. The vaccines give cells instructions for how to make copies of the protein, then the cells destroy the material from the vaccine. Our bodies recognize that the protein should not be there and build white blood cells that will remember how to fight the virus that causes COVID-19 if we are infected in the future.

Nonpharmaceutical Interventions (NPIs)

Actions, apart from getting vaccinated and taking medicine, that help slow the spread of illnesses such as COVID-19. These may include staying home when sick; washing hands; wearing a mask; physical distancing when coming in close contact with others; temporarily closing schools and businesses; and cleaning surfaces.


The worldwide spread of a new disease.


A substance that is given in a clinical trial that does not contain the certain medication or vaccine being studied. The participants in a trial or experiment who are given this placebo are compared to those who receive the vaccine being studied to determine how the vaccine performs compared to those who receive the placebo (such as if those who received the vaccine were less likely to be infected with COVID-19 compared).


The number of disease cases (new and existing) within a population over a given time period.

Principal investigator

The person in charge of a clinical trial. He or she is a scientist who is an expert in what the trial is about. The principal investigator takes the lead in designing a clinical trial, choosing the research team, and carrying out the study.


The process of separating and limiting the movement of people who were exposed to a contagious disease such as COVID-19 to see if they become sick. During that time, those in quarantine are asked to monitor potential symptoms.

R0 (or R-naught)

The average number of people that a person with an infectious disease is expected to spread the infection to. If R0 is greater than 1, it can spread in a population.

Side Effect

Any health problem shown by studies to be caused by a vaccine. Like any medication, vaccines can cause side effects. Usually vaccine side effects are minor (for example, a sore arm where a shot was given or a low-grade fever after a vaccine) and go away on their own within a few days.

Social distancing (also physical distancing)

Putting space between yourself and others to slow down the spread of infection.

Trial protocol

A series of procedures to be carried out during a clinical trial.

Vaccine efficacy (also referred to as efficacy rate)

A measure that is used to describe how good a vaccine is at preventing disease. Efficacy is the benefit that a vaccine provides compared to a placebo, as measured in ideal conditions such as in a clinical trial. To test a coronavirus vaccine, for instance, researchers compare how many people in the vaccinated and placebo groups get Covid-19. A vaccine efficacy of 90% means a 90% reduction of the number of cases from what would have occurred if the participants had not been vaccinated. The greater the percentage reduction of illness in the vaccinated group, the greater the vaccine efficacy.

Vaccine effectiveness

The benefit that a vaccine or a drug provides out in the real world (compared to the benefit found in the controlled conditions of a clinical trial). A vaccine effectiveness of 90% means that there was a 90% reduction of the number of cases that would have occurred if they had not been vaccinated. The greater the percentage reduction of illness in the vaccinated group, the greater the vaccine effectiveness. A vaccine’s effectiveness may turn out to be lower or higher than its efficacy.


A way of protecting the body against disease by injecting a substance (often containing all or part of a microorganism, such as a virus) that will cause the body to develop antibodies against the microorganism and later fight off disease.

Vaccine hesitancy

Vaccine hesitancy refers people delaying or refusing of to get vaccinated despite the availability of a safe vaccine.

Viral load

The amount of a virus in a sample, especially a person’s blood or other bodily fluids. Viral load is typically measured as the number of virus particles per milliliter.


A tiny organism that multiplies within cells and causes disease such as COVID-19, chickenpox, measles, mumps, rubella, pertussis and hepatitis. Viruses are different from bacteria; viruses are smaller, have a different structure, and cause different diseases than bacteria. Viruses are not affected by antibiotics, the drugs used to kill bacteria.

White blood cells

Blood cells that protect the body from infection.

Zoonotic disease

A disease that has its source from an animal that is communicable to humans. COVID-19 is believed to be a zoonotic disease.

Health/ स्वास्थ्य

Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity. (WHO)

स्वास्थ्य पूर्ण शारीरिक, मानसिक और सामाजिक कल्याण की अवस्था है, न कि केवल बीमारी या दुर्बलता की अनुपस्थिति। (WHO)

Public Health/ लोक स्वास्थ्य

Public health focuses on groups of people, rather than just an individual. At the core of public health lies the principle of social justice, providing people the right to be healthy and to live in conditions that will support their health.

लोक स्वास्थ्य केवल एक व्यक्ति के बजाय लोगों के समूहों पर केंद्रित है। लोक स्वास्थ्य के मूल में सामाजिक न्याय का सिद्धांत निहित होता है, जिसमें लोगों को स्वस्थ रहने और उनके स्वास्थ्य का सहयोग करने वाली परिस्थिति में जीने का अधिकार होता है।

Social determinants of Health/ स्वास्थ्य के सामाजिक निर्धारक

Social determinants of Health are the conditions in which people are born, grow, live, work, worship and age that affect their health and well-being.

ये लोगों के स्वास्थ्य और आरोग्य को प्रभावित करने वाली वे परिस्थितियां हैं जिनमें लोग पैदा होते हैं, बढ़ते हैं, जीते हैं, काम करते हैं, उपासना करते हैं और बूढ़े होते हैं।

Misinformation/ झूठी सूचना

Incorrect or misleading information inadvertently sent in order to influence public opinion or obscure the truth.

अनजाने में गलत सूचना फैलाकर जनता की राय को प्रभावित करना।

Disinformation/ दुष्प्रचार

False information deliberately and often covertly spread in order to influence public opinion or obscure the truth.

जानबूझ कर गलत सूचना फैलाकर जनता की राय को प्रभावित करना।

Epidemiology/ महामारी विज्ञान

Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.

यह जनसंख्या विशेष में स्वास्थ्य संबंधी परिस्थितियों या घटनाओं (बीमारी या मृत्यु) के प्रसार और उससे होने वाले नुकसान का अध्ययन है, जिसका उपयोग स्वास्थ्य संबंधी समस्याओं के नियंत्रण के लिए किया जाता है।

Rate/ दर

Rate measures the occurrence of some particular event (development of disease or the occurrence of death) in a population during a given time period.

यह किसी तय समयावधि के दौरान किसी जनसंख्या विशेष में किसी खास घटना (बीमारियों या मृत्यु के होने) की आवृत्ति का माप है।

Ratio/ अनुपात

Ratio is the relationship between two numbers showing how many times one number contains the other, to compare their relative size.

दो संख्याओं के बीच संबंध, जो यह दर्शाता हो कि एक संख्या में दूसरी संख्या का मान कितनी बार आता है, ताकि दोनों के आकार का तुलनात्मक बोध हो सके।

Proportion/ अंश

Proportion is a ratio which indicates the relation in magnitude of a part of the whole.

यह ऐसा अनुपात है जो संपूर्ण के मुकाबले उसके किसी हिस्से के आकार को प्रदर्शित करता है।

Mean/ मध्य

Mean is the arithmetic average of a set of values i.e. a sum of all value, divided by the total number of values.

यह कई मानों के समूह का अंकगणितीय औसत है। अक्सर सभी मान या मूल्यों को जोड़ कर उनकी कुल संख्या से भाग देने से हासिल होने वाली संख्या को मध्य माना जाता है।

Median/ माध्यिका या मध्य मूल्य

Median is the middle piece of data, after you have sorted data from the smallest to the largest.

इसमें आंकड़ों को पहले छोटे से बड़े के क्रम में लिखा जाता है और फिर उसका मध्य हासिल किया जाता है। बहुत असमानता वाले आंकड़ों का ज़्यादा वास्तविक मध्य मूल्य हासिल करने के लिए मध्य की बजाय माध्यिका का उपयोग होता है।

Mode/ मोड

Mode is the value that repeats most often.

आंकड़ों या मूल्यों के समूह में सबसे अधिक बार आने वाला मूल्य या आंकड़ा।

Prevalence/ व्यापकता

Prevalence is the proportion of people in a population who have some health attribute or condition at a given point in time or during a specified period.

यह किसी जनसंख्या में किसी खास समय पर या समयावधि के दौरान किसी खास स्वास्थ्य संबंधी कारक या अवस्था से युक्त लोगों का अनुपात है। किसी बीमारी से निपटने के लिए जब सरकार या कोई एजेंसी अपना कार्यक्रम बनाती है तो वह सिर्फ नए सामने आ रहे मामले ही नहीं बल्कि उसके कुल प्रसार या व्यापकता को ध्यान में रखती है।

Incidence/ आपतन या नए मामले

Incidence is the number of new events (for example, new cases of a disease) in a defined population, occurring within a specified period.

किसी तय जनसंख्या में किसी खास समयावधि के दौरान सामने आए नए मामले (जैसे कि किसी बीमारी के नए रोगियों की संख्या)। आम तौर पर किसी बीमारी को सीमित करने के प्रयासों के प्रभाव का आकलन करने में यह संख्या उपयोगी होती है। इससे पता चल जाता है कि संबंधित बीमारी का प्रकोप वास्तव में कम हो रहा है या बढ़ रहा है।

Morbidity/ रुग्णता संख्या

किसी जनसंख्या, क्षेत्र या किसी अन्य विशेष समूह में किसी बीमारी के नए मामले या कुल मामलों की गणना।

Mortality/ मृत्यु संख्या

किसी जनसंख्या, क्षेत्र या अन्य विशेष समूह में किसी खास रोग की वजह से होने वाली मृत्यु की गणना।

Risk Factors/ जोखिम के कारक

किसी स्वास्थ्य समस्या या समस्याओं की आशंका के बढ़ने के लिए जवाबदेह व्यक्तिगत विशेषताएं या सामाजिक परिस्थितियां।

Epidemic/ महामारी

Epidemic is the occurrence of more than expected cases of disease, injury, or other health conditions in a given area or among a specific group of persons during a particular period. Usually, the cases are presumed to have a common cause or to be related to one another in some way.

किसी खास समयावधि के दौरान किसी खास क्षेत्र या विशेष समूह में किसी बीमारी, चोट या अन्य स्वास्थ्य समस्याओं के अनुमान से काफी अधिक होने की स्थिति। ऐसी परिस्थिति में आम तौर पर माना गया होता है कि उन मामलों का कारण एक ही होगा या फिर एक-दूसरे से किसी तरह जुड़ा होगा।

Outbreak/ प्रकोप

Outbreak is the occurrence of more cases of disease, injury, or other health conditions than expected in a given area or among a specific group of persons during a specific period. Usually, the cases are presumed to have a common cause or to be related to one another in some way. Sometimes distinguished from an epidemic as more localized, or the term less likely to evoke public panic.

किसी खास समयावधि के दौरान किसी खास क्षेत्र या विशेष समूह में किसी बीमारी, चोट या अन्य स्वास्थ्य समस्याओं की अनुमान से अधिक होने की स्थिति। ऐसी परिस्थिति में आम तौर पर माना गया होता है कि उन मामलों का कारण एक ही होगा या फिर एक-दूसरे से किसी तरह जुड़ा होगा। यह महामारी के मुकाबले में ज़्यादा स्थानीय होता है। महामारी की तुलना में यह शब्द लोगों में कम घबराहट पैदा करता है।

Pandemic/ अतिव्यापी महामारी

Pandemic is an epidemic occurring over a widespread area (multiple countries or continents) and usually affecting a substantial proportion of the population.

यह ऐसी महामारी है जिसका प्रकोप बहुत बड़े क्षेत्र (बहुत से देश या महाद्वीप) में हो और आम तौर पर जो उस इलाके की बड़ी आबादी को प्रभावित कर रही हो।

Endemic / स्थान विशेष की महामारी

Endemic is the constant presence of an agent or health condition within a given geographic area or population; it can also refer to the usual prevalence of an agent or condition.

किसी विशेष क्षेत्र या जनसंख्या में किसी खास स्वास्थ्य समस्या या कारक की लगातार बनी रहने वाली उपस्थिति। इससे किसी स्वास्थ्य स्थिति या समस्या के सामान्य प्रसार या व्यापकता का भी बोध होता है।

Case-Control Study/ केस कंट्रोल अध्ययन

A Case Control study compares a group of participants who have the outcome (cases) with a group of participants who do not have the outcome (controls).

इसमें ऐसे दो समूहों का तुलनात्मक अध्ययन किया जाता है, जिनमें पहले समूह के बारे में ज्ञात हो कि वह संबंधित बीमारी या अवस्था से ग्रसित है जबकि दूसरा समूह इससे मुक्त हो।

Cohort Study/ कोहॉर्ट अध्ययन

A Cohort study follows a group of participants who are at risk for an outcome (retrospectively or prospectively).

इस अध्ययन में जनसंख्या के एक ऐसे वर्ग का निश्चित अवधि के दौरान कुछ अंतरालों के बाद अनुसरण किया जाता है जो संबंधित अवस्था या बीमारी के खतरे की जद में हो।

Cross-Sectional Study/ क्रॉस-सेक्शनल अध्ययन

A Cross-Sectional Study collects all data at a single point in time.

एक अवसर पर या कई अवसरों पर अलग-अलग आबादी पर अध्ययन करना।

Randomized Control Trial/ यादृच्छिक नियंत्रण परीक्षण

A Randomized Control Trial is one where researchers intervene to change the independent variable and assign participants randomly to treatment or control condition

यह ऐसा अध्ययन है जिसमें बिना किसी नियत पैमाने के प्रतिभागियों को भिन्न उपचार या उपाय प्राप्त करने के लिए अध्ययन समूह में शामिल किया जाता है। अध्ययन के लिए कई बार इस समूह पर सामान्य उपचार के अलावा प्लेसिबो यानी छद्म दवा का भी उपयोग किया जाता है। या कई बार उपचार से उन्हें पूरी तरह दूर रखा जाता है।

Systematic Review/ व्यवस्थित समीक्षा

Systematic review is a method of identifying, appraising, and synthesizing research evidence. The aim is to evaluate and interpret all available research that is relevant to a particular review question.

यह शोध साक्ष्यों की पहचान, मूल्यांकन और संश्लेषण करने की पद्धति है। इसका लक्ष्य किसी खास समीक्षा प्रश्न के लिए उपयोगी सभी उपलब्ध शोध का आकलन और विवेचन है।

Meta-analysis/ मेटा-विश्लेषण

Meta-analysis is an examination of data from a number of independent studies of the same subject, in order to determine overall trends.

किसी विषय पर कई शोधों के आंकड़ों को मिलाकर अपना निष्कर्ष करना ।

Correlation/ सहसंबंध

Correlation is the statistical association of one variable with another.

यह एक परिवर्ती कारक का दूसरे के साथ आपस में सांख्यिकीय संबंध है।

Causation/ कारणीय संबंध

Causation is when one variable is at least partially responsible for the second variable; when changes in one variable cause changes in another variable.

जब एक परिवर्ती कारक कम से कम आंशिक रूप से दूसरे परिवर्ती कारक के लिए जवाबदेह हो; जब एक परिवर्ती कारक में बदलाव दूसरे में भी बदलाव लाता हो।

Confounding/ संकरण

Confounding is when a variable influences both the independent variable and the dependent variable, causing a false association between the two.

जब एक परिवर्ती कारक उस पर आश्रित परिवर्ती कारक को तो प्रभावित करता ही है, अनाश्रित परिवर्ती कारक को भी प्रभावित करता है- जिससे दोनों के बीच छद्म अन्योन्याश्रय संबंध पैदा हो जाते हैं।

Validity/ वैधता

Validity is the adequacy and trustworthiness of study findings.

यह किसी शोध के निष्कर्षों की उपयुक्तता और विश्वसनीयता है।

Sources: Definitions were drawn from a number of sources to create this glossary, including the links below: