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Herd Immunity

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Herd immunity is nothing but indirect protection from an infectious disease that can work only for a few diseases. To know more about herd immunity, read the article below.

Medically reviewed by

Dr. C. Elanchezhian

Published At April 29, 2021
Reviewed AtFebruary 20, 2023

What Does Herd Immunity Mean?

Herd immunity is described as when a large part of the population of an area is immune to a specific disease. It is also known as population immunity. It is indirect protection from an infectious disease that happens when a population is immune. There are two ways to achieve herd immunity:

  • Either through vaccination.

  • Through immunity developed from the previous infection.

How Was Herd Immunity Developed?

A simple theoretical theorem was developed by Smith in 1970 and Dietz in 1975, that if immunity were delivered on a random basis and if members on a random basis contacted individuals in a manner sufficient to transmit the infection, then the incidence of infection would decline if the proportion of immunity exceeded.

Though an important paper by Fox et al. in 1971 argued that emphasis on simple thresholds was not appropriate for public health, this herd immunity was used as a target for immunization coverage. Its achievement led to the eradication of infections.

How Does Herd Immunity Work?

Usually, transmittable infections spread from one person to another person. When a proportion of the population is vaccinated, then the spread of the disease slows down. This breaks the chain of transmission. This helps to protect the people who are not vaccinated or who have weakened immunity, or those who are easily susceptible to infections such as:

  • Older adults.

  • Infants.

  • Pregnant women.

  • People with other comorbid health conditions.

What Are the Examples of Herd Immunity?

The classic examples of herd immunity are measles, mumps, rubella, pertussis, chickenpox, and polio. Examples of indirect protection are the introduction of conjugate vaccines against Pneumococcal and Haemophilus infections. The conjugate vaccines are capable of not only protecting the disease but also against the nasal carriage and hence infectiousness. People in Norway successfully developed partial herd immunity to the H1N1 virus, the virus causing swine flu through vaccinations and natural immunity.

Herd immunity works for only some diseases. It does not work for every disease, for example, diseases like tetanus do not spread from one person to another person. Hence tetanus can be prevented only by individual vaccination.

How Can Herd Immunity Work As a Way for Fighting Against COVID-19?

World Health Organization supports achieving herd immunity through vaccination and not by allowing the COVID-19 disease to spread through the population as this would lead to deaths. Vaccines train the immune system to create antibodies that can fight the disease, just as how it would happen when we are exposed to the disease, but without making us sick.

Vaccinated people are protected from the disease, so they do not pass the pathogen. Hence this breaks the chain of transmission, which reduces the spread of the disease.

In order to achieve herd immunity against COVID-19, a proportion of the population needs to be vaccinated. It is estimated that to get protection or herd immunity for the COVID-19 virus, and a person should get infected with the virus and vaccinated. Reinfection is possible in cases of patient who has already tested positive for COVID in the previous waves. It is highly recommended for everyone to get vaccinated. In some areas, most people object to getting a COVID-19 vaccine because of religious objections. If the count of vaccinated people in a community is less herd immunity will be compromised, and this contagious disease could continue to spread the infection. Recent studies have also suggested that people who got infected with the COVID-19 virus in previous years and then received mRNA vaccines which eventually help in the production of very high levels of antibodies that are most likely to affect the current and future variants. Some scientists or doctors named it hybrid immunity. Though it required further research.

How Many People Need To Be Vaccinated to Achieve Herd Immunity to COVID-19?

The proportion of people who need to be vaccinated varies with each disease. For example:

  • For measles, the percentage of people to be vaccinated is about 95% of the population. In contrast, the remaining 5% of the population will be protected by the fact that measles will not spread among the vaccinated people.

  • For polio, the percentage of people who need to be vaccinated is 80%.

  • For COVID-19, the percentage of the population to be fully vaccinated in order to achieve herd immunity is still counting. This is an important part of the study and research and will likely vary according to the community and populations prioritized for vaccination, various other factors. However, World”s Health Organisation supports achieving herd immunity by vaccination, not by getting affected by the COVID-19 infection.

Achieving herd immunity will save many lives and will prevent the COVID-19 disease from spreading.

Why Is Herd Immunity Still Not Possible For COVID-19?

  • To develop a herd immunity people start taking the vaccination seriously and follow the safety precautions and guidelines.

  • Antivirals specific for COVID-19 are still under research. Meanwhile, drugs like Remdesivir, Nirmatrelvir with Ritonavir, and Molnupiravir are recommended antiviral drugs used for the treatment of COVID-19.

  • If too many people test positive for COVID-19, healthcare systems and hospitals cannot handle the situation. This can cause serious collateral damage to the existing health system.

  • Research is still going on about why certain people develop serious complications while others do not.

  • People who are infected with the COVID-19 virus can develop life-threatening symptoms, which can even lead to death. The vulnerable members of society, such as the elderly or those with comorbid health conditions, are more at risk. Healthy people can also fall ill from exposure to the virus.

These are the reasons why herd immunity is still impossible.

The main goal of herd immunity is to stop the spread of any disease. Stopping the spread can save many lives. It can help people who cannot be vaccinated. To achieve herd immunity is through vaccination. The percentage of the population to be vaccinated in the case of COVID-19 for achieving herd immunity is still under study. However, until the data are conclusive, herd immunity cannot be implemented. Hence, herd immunity is still not the way to fight COVID-19. Hence health experts worldwide suggest that the best way to prevent COVID-19 disease is to follow the guidelines.

These are some of the preventive tips that have to be followed:

  • Do wear a mask when in public.

  • Maintain social distance.

  • Avoid gatherings.

  • Wash your hands frequently with soap and water.

  • Do not keep touching your nose and mouth.

  • If you notice the symptoms, please keep yourselves isolated and contact health experts.


The spread of diseases like COVID-19 is prevented completely through community vaccination. Hence, increasing awareness among people about the COVID-19 vaccination is essential. However, the percentage of people to be vaccinated to achieve herd immunity is still under investigation. As of now, it is advisable to follow the COVID-19 safety guidelines to prevent its spread. For further information, you can consult doctors on icliniq.

Frequently Asked Questions


What Is Herd Immunity?

Herd immunity, also called innate immunity, happens when a large portion of the population of an area develops immunity to a specific disease. It is also known as population immunity. It indirectly protects against an infectious disease when a population is immune.


What Are the Types of Immunity?

- Active immunity occurs when exposure to a disease organism activates the immune system to produce antibodies to that disease. This immunity can be acquired through natural immunity or vaccine-induced immunity.
- Natural immunity naturally exists. It happens through exposure to the disease organism or infection with the actual disease.
- Vaccine-induced immunity is acquired by introducing a weakened or killed form of the disease organism through vaccination.
- Passive immunity happens when people receive antibodies to pathogens rather than produce them through their immune system.


How Is Herd Immunity Achieved?

When a proportion of the population is vaccinated, the spread of the disease slows down. This breaks the chain of transmission. This helps to protect people who are not vaccinated, who have weakened immunity, or who are easily susceptible to infections, such as:
- Older adults.
- Infants.
- Pregnant women.
- People with other comorbid health conditions.


Can Someone Get COVID More Than Once?

Yes, one can get COVID-19 more than once. There are various reasons behind reinfection, including:
- Vaccine immunity diminishes with time.
- The pandemic has been happening for a while.
- People have stopped being as vigilant as they were in the initial days.
- New variants are extra-contagious.


How Long Does It Take To Recover Completely From COVID-19?

The recovery period generally depends on the severity of the illness. People with mild cases can expect to recover within about two weeks. But it could take months for more severe cases to feel better, and hospitalization might be required.


Is There a Natural Immunity to Omicron?

In experiments using mice and blood samples from donors infected with Omicron, it was found that the Omicron variant induces only a weak immune response.


How Long Does COVID-19 Survive in the Air?

A study found that the coronavirus can survive in aerosol form for 3 hours.


How Long Does the mRNA Vaccine Stay In the Body?

mRNA degrades in the body naturally after a few days, and the spike protein it makes only stays for a couple of weeks.


Is Sneezing a Symptom of Omicron?

Although initially not considered a prominent COVID-19 symptom, it is commonly found in people with the omicron variant.
Common Omicron variant COVID-19 symptoms include:
- Runny nose
- Headache
- Fatigue
- Sneezing
- Sore throat


Are There People Who Cannot Get COVID-19?

With COVID-19, researchers have yet to discover a genetic mutation that makes anyone completely immune.
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Dr. C. Elanchezhian
Dr. C. Elanchezhian

General Medicine


herd immunity
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