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Coronavirus Explainers

Coronavirus Vaccine Glossary: 15 Terms To Know About Vaccination

Here is a glossary of terms related to vaccines to help learn all about the COVID-19 vaccine and vaccination in general

Coronavirus Vaccine Glossary 15 Terms To Know About Vaccination
  • The outer layer of Coronavirus is called spike protein
  • Vaccines using killed version of a virus are called killed vaccines
  • Antibodies are the immune response produced by a human body

New Delhi: From not knowing anything about the Novel (new) Coronavirus a year ago to rolling out vaccines against the COVID-19 disease causing virus, the world has come a long way in the fight against the pandemic in record time. Currently there are eight COVID-19 vaccines that have got emergency use license and are being administered in over 70 countries. These vaccines are Oxford-AstraZeneca’s Covishield; Bharat Biotech’s Covaxin; Gamaleya Research Institute’s Sputnik V; Pfizer-BioNTech’s BNT162b2; Moderna’s mRNA-1273; Sinovac’s CoronaVac; Sinopharm’s two COVID-19 vaccines.

Also Read: Coronavirus Explainer: What Is A Sero Survey And Why Is It Important In The Fight Against COVID-19?

India has already vaccinated 58.12 lakh people since the vaccination drive began on January 16. The two vaccines that are part of this drive are Oxford-AstraZeneca’s Covishield and Bharat Biotech’s Covaxin. The country is manufacturing two vaccines and is exporting both the vaccines to 14 nations. India is one of the largest vaccine producers in the world covering 60 per cent of the global vaccine production. There is one more vaccine contender waiting in the wings – Russian COVID-19 vaccine Sputnik V which is likely to apply for emergency use license in March. Serum Institute of India is hopeful of launching another vaccine Covovax – developed in partnership with American vaccine developer Novavax – in India by June 2021.

Also Read: Coronavirus Vaccine Explainer: How Effective Is Novavax Vaccine? When Will It Be Launched In India?

Each of these vaccines follows a different route to fight the Coronavirus. So here is a glossary of terms related to vaccines to help learn all about the COVID-19 vaccine and vaccination in general.

Active Immunity

Active immunity is the immunity generated after exposure to a disease organism. In layman’s term, when an individual is exposed to a disease like COVID-19, the human body produces antibodies, an immune response to fight back the disease.

Exposure to the disease organism can occur through infection with the actual disease (resulting in natural immunity), or the introduction of a killed or weakened form of the disease organism through vaccination (vaccine-induced immunity). Either way, if an immune person comes into contact with that disease in the future, their immune system will recognise it and immediately produce the antibodies needed to fight it. Active immunity is long-lasting, and sometimes life-long, states United States’ Centers for Disease Control and Prevention (CDC).

However, in the case of COVID-19, we don’t know for how long the natural immunity lasts. According to the experts and studies, immunity may last for six months.

Also Read: COVID-19 Vaccine: WHO Expert Answers Frequently Asked Questions

Adverse Event Following Immunisation (AEFI)

World Health Organisation defines Adverse Event Following Immunisation (AEFI) as any untoward medical occurrence which follows immunisation and which does not necessarily have a causal relationship with the usage of the vaccine.

If not rapidly and effectively dealt with, (AEFI) can undermine confidence in a vaccine and ultimately have dramatic consequences for immunisation coverage and disease incidence, says WHO.

Also Read: Coronavirus Explainer: What Are Adverse Events Post COVID-19 Immunisation


Dr Hanan Balkhy, WHO Assistant Director-General for Antimicrobial Resistance defines antibodies as immune response produced by a human body against specific antigens – proteins that exist on the outer shell of the virus itself. There are two kinds of antibodies – IgM (Immunoglobulin M) and IgG (Immunoglobulin G).

While IgM develops at an early phase of the infection, typically after the first week of contracting the virus, IgG antibodies are more likely to show up later – when an individual has recovered from the infection. IgM disappears after six weeks whereas IgG stays on for a longer period of time. However, as of now, it is not clear for how long IgG gives immunity against COVID-19.

Also Read: Coronavirus Outbreak Explained: What Is Antibody Test And What Role Does It Play In The Fight Against COVID-19?


Immunisation is the process of protecting an individual from disease. A person can be immunised through vaccination (an injection) against a disease that helps in developing an immune response. Immunisation is recognised as one of the world’s most successful and cost-effective health interventions for saving lives.

Killed Or Inactivated Vaccine

The disease carrying virus, in the case of COVID-19 it is SARS-CoV-2, is inactivated or killed using chemicals, heat or radiation and then injected.

Inactivated vaccines have been around for ages and one example is polio vaccine. They can be manufactured on a large scale, said Dr Harsh Mahajan, Founder Of Mahajan Imaging and Chairman of CARINGdx.

Covaxin, COVID-19 vaccine being produced by Bharat Biotech and the Indian Council of Medical Research in India is an inactivated vaccine.

Also Read: Vaccine Hesitancy: What It Means And How We Can Tackle It, Experts Explain

Live Attenuated Vaccine

The live-attenuated vaccine uses a living but weakened version of the virus or one that’s very similar. The virus is weakened to an extent where it does not cause serious disease. Explaining how this vaccine produces an immune response, Dr K K Aggarwal, President, Heart Care Foundation of India (HCFI) and Confederation of Medical Associations of Asia and Oceania (CMAAO), said,

Let us say I have thrown a non-poisonous snake in your house. You don’t know it is harmless. What will be your reaction? You will get scared, panic and find ways to protect yourself from the snake. Similarly, when a live but weakened virus is injected into our body by the means of vaccine, our body starts to fight it. For the human body, it is a virus regardless of whether or not it is harmful.

The measles, mumps and rubella (MMR) vaccine and the chickenpox and shingles vaccine are examples of this type of vaccine.

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Memory Cells

Memory cells are a group of cells that help the body fight a disease by remembering a prior exposure to a same disease or disease causing virus. T-cells and B-cells are called memory cells and they can retain the memory of infection for life; even after antibodies have faded. However, in the case of the COVID-19, we don’t know for how long these cells retain memory.

Explaining the working of memory cells, Dr Ravindra M Mehta, Senior Consultant and HOD – Pulmonology and Interventional pulmonology, Apollo Speciality Hospitals Jayanagar, said,

When you meet or see someone for the first time, you see their face and your mind captures it. When you meet the same person second time, it is easier for you to recognise that person because your mind already has an image of that person. Similarly, when the human body is exposed to a virus either naturally or through vaccines, memory cells remember the infection. When an individual is exposed to the virus again, memory cells can trigger a faster and stronger immune response.

Also Read: Coronavirus Outbreak Explained: What Is T-Cell Immunity And How Does It Provide Defense Against COVID-19?

mRNA Vaccine

mRNA or messenger-RNA vaccines use specific parts of the infectious agent like its protein, sugar, or coating to produce an immune response. These vaccines give a message to our cells to make a protein or even just a piece of a protein which are like those of the SARS-CoV-2 virus. The protein then triggers an immune response inside our bodies. That immune response, which produces antibodies, is what protects us from getting infected if the real virus enters our bodies.

Because these vaccines use very specific regions, they offer a strong immune response targeting specific regions of the infective agent. They can be used on almost everyone, including those with compromised immunity, said Dr Rajesh Parikh, Director, Medical Research at Jaslok Hospital and the author of ‘The Vaccine Book for COVID-19’.

Vaccines being produced by Pfizer-BioNTech and Moderna are based on mRNA vaccine technology.

Also Read: Coronavirus Outbreak Explained: What Is mRNA COVID-19 Vaccine Technology Used By Pfizer-BioNTech And Moderna?


A mutation is a change in the genome or genetic sequence of a virus which results in a new strain of the virus. Explaining mutation, Dr. Preeti Kumar, Vice President, Public Health System Support at the Public Health Foundation of India said,

Mutation is the property of a virus to undergo changes when it multiplies. As it replicates, it may not produce exact replicas of itself, resulting in the emergence of new strains, which may be more or at times less effective. Some strains die out, while the more effective ones which spread efficiently, survive.

Also Read: COVID-19 Outbreak Explained: What Is Coronavirus Mutation And What Are The Dangers?

Passive Immunity

Passive immunity is provided when a person is given antibodies to a disease rather than producing them through his or her own immune system. A newborn baby acquires passive immunity from its mother through the placenta, explains CDC.

An individual can also get immunity through antibody carrying blood product. In the case of COVID-19, plasma therapy acts as a way to provide passive immunity. Blood plasma containing antibodies from a recovered COVID-19 patient is given to a critically ill COVID-19 patient to initiate an immune response.

As per CDC, passive immunity provides immediate protection and lasts only for a few weeks or months.

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Sometimes people psychologically feel better just because they are taking a medicine. Similarly, often people imagine side-effects. To remove that psychological effect in any trial you compare a real drug with an inactive substance. In vaccine trials that inactive substance might just be distilled water, explained Dr Parikh.

Placebo is an inactive drug or inert vaccine given to some of the trial participants. During randomised clinical trial, participants are randomly given the vaccine being tried and inert vaccine without them knowing what is being administered to them.

If it is a randomized double blind clinical trial it means randomly participants are divided in two groups – experimental group and placebo. Double blind means both the receiver and the people involved in the research – scientists, clinicians, doctors, nurses, and others are unaware of the intervention – vaccine or placebo – being administered to the participants, detailed Dr Mehta.

At the end of the trials, efficacy and safety is assessed among both groups.

Also Read: Coronavirus Explained: What Are The Phases In The Clinical Trials Of The COVID-19 Vaccine?

Spike Protein

The outer layer of the virus; the spikes on the virus are called spike protein. Dr Parikh defines spike protein as a key and human cell receptor as a lock. Cells without this receptor are safe as spike protein cannot unlock them. When the spike protein opens the lock, the coronavirus can enter and infect the cell. Once the lock is opened, the coronavirus’ viral envelope open and the content gets mixed with the human cell.


The CDC defines strain as a specific version of an organism. Many diseases, including HIV/AIDS and hepatitis, have multiple strains. In the case of COVID-19, currently, two new strains of SARS-CoV-2 have been reported from the United Kingdom and South Africa. According to WHO’s Chief Scientist Dr Soumya Swaminathan, the two particular variants that have been reported to WHO have one change in common and that is called N501Y mutation. But otherwise the two are different.

Also Read: COVID-19 Outbreak Explained: What Do We Know So Far About The New Coronavirus Strains Detected In The United Kingdom And South Africa

Dr Swaminathan asserted that possible mutations are kept in mind while developing a vaccine as some vaccines need to be updated with the change in the strain of the virus. For example, the structure of the vaccine against influenza virus needs to be changed every year based on the circulating strains.

Vaccine Efficacy

As per WHO, vaccine efficacy is the percentage reduction in disease incidence among people who received vaccine in a clinical trial compared to people who didn’t.

Viral Vector Vaccine

Viral vector vaccine uses a safe virus to deliver specific sub-parts – called proteins – of the germ of interest so that it can trigger an immune response without causing disease, explains WHO.

Oxford-AstraZeneca’s COVID-19 vaccine Covishield which is currently being used in India is a viral vector vaccine. It is a genetically modified vaccine where a part of the SARS-CoV-2 specifically the spike protein is added to a modified version of a chimpanzee adenovirus, known as ChAdOx1. Chimpanzee adenovirus is a harmless, weakened adenovirus that usually causes the common cold in chimpanzees.

Explaining how chimpanzee adenovirus helps fight Coronavirus, Dr Parikh said,

The adenovirus acts as a vehicle known as a vector to transport the spike protein into the human cell which will then trigger the immune response. It is genetically modified so that it cannot replicate.

Also Read: Vaccine Explainer: How Does Immunisation Protect Against A Disease?

NDTV – Dettol Banega Swasth India campaign is an extension of the five-year-old Banega Swachh India initiative helmed by Campaign Ambassador Amitabh Bachchan. It aims to spread awareness about critical health issues facing the country. In wake of the current COVID-19 pandemic, the need for WASH (WaterSanitation and Hygiene) is reaffirmed as handwashing is one of the ways to prevent Coronavirus infection and other diseases. The campaign highlights the importance of nutrition and healthcare for women and children to prevent maternal and child mortality, fight malnutrition, stunting, wasting, anaemia and disease prevention through vaccines. Importance of programmes like Public Distribution System (PDS), Mid-day Meal Scheme, POSHAN Abhiyan and the role of Aganwadis and ASHA workers are also covered. Only a Swachh or clean India where toilets are used and open defecation free (ODF) status achieved as part of the Swachh Bharat Abhiyan launched by Prime Minister Narendra Modi in 2014, can eradicate diseases like diahorrea and become a Swasth or healthy India. The campaign will continue to cover issues like air pollutionwaste managementplastic banmanual scavenging and sanitation workers and menstrual hygiene


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