What is herd immunity, antibody and antigen in Covid-19


herd immunity, antibody, asymtomatic COVID19

In the era of COVID-19 pandemic we came across the many scientific and medical terms such is antibody, herd immunity, asymptomatic, etc. These words are not new for those who are related to the medical field. But for common people, these are new words.

We had a discussion of all these terms in the form of questions and answers with Dr. Pratik Savaj who is an infectious disease specialist providing his expert service in the Surat city of Gujarat, India. Let’s understand all these terms and other information to be useful for all people in simple language.

 Herd Immunity 

What is herd immunity?

Simply you can say ‘herd’ means group. Herd immunity means immunity of the community. When many people in a community develop immunity against an infectious agent that helps to stop the disease from spreading.

For example in a home there live seven peoples including a small child also. To prevent an infectious disease to this little one, another six members of the family will be vaccinated. So that little child will not be infected.

The best way to develop herd immunity is vaccination. Mass vaccination in one day or one week will develop immunity. As we do vaccination for polio to prevent it.

Is it possible to have herd immunity without a single person being infected?

No. It is not possible. To develop natural herd immunity majority of the people say almost more than 70% should get infected with COVID-19 without vaccination.

How herd immunity will help in case of COVID-19 even no vaccine is there?

To develop herd immunity there are only two ways. One is many people get infected or contracted with COVID-19 disease to build up natural immunity and another way is the vaccine.

Should the government be in favor of herd immunity?

There may be many cases of COVID-19 with no symptoms. these are asymptomatic cases. As time passes the people develop immunity against COVID-19 and the level of immunity increases.

For example, initially, there will be 20% of people with herd immunity against COVID-19. This will increase to 25%, 30% and so on. We can hope that people will get immunity with common symptoms.

The concept of herd immunity was applied by United Kingdom (UK) but they got troubled and COVID-19 cases were increased. So, the Indian government is not in favor of herd immunity at present.

What will happen to whose immunity is weak, if concept of herd immunity is applied?

People above the age of 60 with other conditions like diabetes, hypertension, etc. may be affected severely and also the danger of life for them.

Herd immunity means let people get infected with COVID-19 by allowing them for get-togethers, meetings, parties and let them develop natural immunity. But people with low immunity will be in trouble, their lungs will be affected severely and may need ventilators. That’s why this way of developing natural immunity is fatal.

In COVID-19 disease, 10% out of 100% people will be affected seriously and 90% will be with normal symptoms. At first sight, this looks good but 10% of people may lose their lives. This policy is not good. So United Kingdom withdraw the concept of developing natural immunity without vaccination after taking a wrong step.

How long does it take for the virus to weaken after developing a herd immunity and antibody?

The virus will not be weakened. But it will be mutated means the change in the gene structure of the virus.

Virus is also intelligent. If there is big change in virus it is called antigenic shift and if the change is small it is called antigenic drift.

What will happen if there is antigenic shift and antigenic drift of the virus?

In big structural change means in case of antigenic shift, the virus will become new. So the condition will be new for us and we have to start again from one.

Is COVID-19 is antigenic shift of the SARS virus?

Yes. New COVID-19 is totally different from SARS coronavirus or SARS-Cov-1.


What is asymptomatic?

COVID-19 does not affect with serious symptoms to all. In fact, there may be no symptoms even if infected with COVID-19. These cases are called asymptomatic cases.

How can asymptomatic cases can infect others?

By chance, if asymptomatic cases of COVID-19 sneezes or coughs, they may infect others.

 Antibody and Antigen 

How many types of tests are there for the diagnosis of COVID-19?

There are antigen test and antibody test for diagnosis of COVID-19.

What is the antigen and antibody test?

Identification of the genetic structure of coronavirus is called antigen test. It is also known as RT-PCR (reverse transcription-polymerase chain reaction). Sample from the nose and throat is taken to perform an antigen test.
An antibody test is performed by testing blood samples. When anyone is infected with COVID-19, he or she develops immunity by protective protein also known as Immunoglobulin (IG). The blood testing of this immunoglobulin is called an antibody test.

How many types of antibody tests are there?

First, our body develops IgM which is the Immunoglobulin M antibody, and after some time develops IgG which is the Immunoglobulin G antibody. These two types of antibody tests are done in the case of COVID-19.
Our body develops IgM after 7 days and IgG nearly after one month.

What is IgM and IgG test indicates?

In the case of COVID-19, if your IgM antibody test is positive then you are already infected with COVID-19. The disease may be active or inactive within you or you are recovered from the disease.
If IgG is positive then you have an antibody prepared to fight against COVID-19. The army is ready. Different viruses have different antibodies in our bodies.

When antigen tests and antibody tests is performed?

Antigen test which is an RT-PCR test is done for diagnosis of COVID-19. This diagnostic test indicates whether the person is COVID-19 positive or not.
For diagnosis of COVID-19 antibody test is not used according to the guideline of the Indian government. At present, it is used for studying epidemiology purposes only. Epidemiology study collects data about how many people developed immunity against COVID-19 so that the government takes the next step to control the disease.

Is the antibody test accurate?

The Indian government doesn’t allow to perform an antibody test initially. Only National institutions are provided an antibody kit to know the immunity data of doctors and health workers. Now anyone can do it.

Who should get an antibody test?

Doctors and health care workers should get an antibody test to know their immunity status of them.

Can it be assumed that if antibodies are made in our body, COVID-19 will no longer be infected?

It depends on the life of the antibody. An antibody of different infectious agents has a different life.
For example, after getting chickenpox disease once, you will not be infected by chickenpox virus again. Because the life of antibody again chickenpox disease lasts lifelong. Likewise, the antibody life of SARS-Cov-1 is also lifelong. The person who was infected with SARS-Cov-1 was never infected with it again. At present, there are no solid data about COVID-19 antibody life. So it is difficult to say anything about COVID-19.

This article is reviewed by

Dr. Pratik Savaj

Infectious disease specialist
SCID-AI (Surat Clinic of Infectious Disease and Adult Immunization)
Surat, Gujarat, India.

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