The WHO does not suggest herd immunity intentionally in a population. However, immunity boosters may be taken to boost the immune system and prevent autoimmune diseases.

Is Herd Immunity The Solution To Our Problems?

Introduction

When archaeologists dig up ancient cities buried under centuries of soil and history, they help uncover the evolution of human civilizations. From Mesopotamia to the Indus Valley, ancient civilizations have made several advances that continue to influence modern-day humans. These range from developments in culture, infrastructure, weapons, astronomy, engineering, printing, and much more. However, as humans built cities and waged wars, they also dealt with deadly pandemics that threatened to wipe out whole civilizations.&nbsp; 
&nbsp;

A pandemic is a name given to an infectious disease that has spread across borders and continents. On the other hand, diseases limited to a given population within an area is called an epidemic. Throughout history, several epidemics and pandemics have affected humans across the world.&nbsp; 
&nbsp;

The Black Death, or bubonic plague, is believed to be the most fatal pandemic in history. Occurring from 1346-1352, the disease is believed to have caused more than 25 million deaths in Europe<a href="#accordion">[1]</a>. However, this was not the first time that a plague caused widespread destruction. Earlier in 541 CE, the Plague of Justinian entered Constantinople and spread across Europe, North Africa, and Asia. It is estimated to have killed half of the world&#39;s population. At that moment in history, not much was known about fighting pandemics, so it is unclear what eventually <a href="https://merisehat.pk/page/sehat-a-z/">caused the disease</a> to die down. Researchers believe that majority of people who survived did so because of their immunity.&nbsp; 
&nbsp;

On the other hand, the spread of the Black Death was controlled through quarantine. The word quarantine was invented by the Venetians who imposed a 40-day isolation rule for all sailors entering the port city of Ragusa. 
&nbsp;

Till the 16th Century, isolating the sick became a part of disease control. It wasn&#39;t until Edward Jenner discovered the smallpox vaccine that vaccinations began to play a role in controlling infections. Prior to his invention, smallpox killed 3 out of every 10 people it infected<a href="#accordion">[2]</a>. Edward Jenner&#39;s experiment paved the way for future vaccines. And in 1980, the World Health Organization (WHO) announced the complete eradication of smallpox thanks to global vaccination programs. However, many researchers argue that herd immunity might have played a significant role in eradicating smallpox from the world. 
&nbsp;

But what is herd immunity? And where did it come from?

&nbsp;

While death and destruction were a common feature of World War I (WWI), several infectious diseases also wreaked havoc among civilians and soldiers. The chaotic wartime conditions characterized by malnourishment and poor hygiene conditions further spread infections among the masses. Moreover, the deadly influenza pandemic, also called Spanish flu, eclipsed the end of the first World War.&nbsp; 
&nbsp;

Thus, worried about the rising infections and looming threat of epidemics, in 1919, bacteriologists W.W.C. Topley and G.S. Wilson at the University of Manchester designed an experimental epidemic model with 15,000 mice<a href="#accordion">[3]</a>.&nbsp;The mice were allowed to move freely among the residential pods connected via tunnels. As part of the experiment, researchers exposed the laboratory mouse city models to deadly bacteria while another city received a vaccine and the bacteria. They noticed that despite not receiving vaccines, susceptible mice remained protected from bacterial infection. Thus, they proposed that immunity to an infection may be achieved if a certain proportion of the population became immune. They called this &quot;herd immunity.&quot;&nbsp; 
&nbsp;

Previously, veterinary scientists in the United States and Britain had used the term to describe the resistance to diseases among animals.&nbsp; 
&nbsp;

Later in the 1930s, researcher A. W. Hedrich used the term herd immunity to describe the decrease in the incidence of measles among children in Baltimore. He noticed that measles outbreaks seem to die down when a large number of children became immune due to a previous infection. Thus, the naturally occurring phenomenon also ended up protecting susceptible children.&nbsp;

&nbsp;

Understanding Herd Immunity And Its Impact On Public Health

Herd immunity results from a large proportion of the population becoming immune to an infectious disease. This reduces the risk of the spread of infection from person to person. As a result, people who are not immune are also protected. For example, if a sick person encounters four people, three of whom are immune to the disease, only one will go on to contract the infection. Moreover, the other three would not spread the disease further. Thus, instead of multiple cases leading to an outbreak, there will be a singular case which is easier to control and poses a lesser threat to public health.

&nbsp;

There are two ways to achieve herd immunity: natural infection and vaccines.&nbsp; 
&nbsp;

In case of a natural infection, the person forms antibodies that protect against future infections. However, these antibodies vary in amount depending on the person&#39;s immune system and provide them protection for a limited period only. Moreover, even if a large proportion of adults in a community develop immunity, the disease may still affect children. Therefore, herd immunity through natural infection is not the most reliable method. 
&nbsp;

Many researchers favor achieving herd immunity with the help of vaccines. They believe widespread vaccination of the population is the best way to achieve herd immunity and eliminate the disease from circulation. Through the introduction of a weakened or killed pathogen, vaccines induce an immune response in the body. Unlike a natural infection, vaccines can create immunity without the illness or risk of mortality and morbidity.&nbsp; 
&nbsp;

Over the years, several diseases have been controlled thanks to the vaccine herd effect. Vaccination against H. influenzae type b, pertussis, streptococcus pneumoniae, seasonal influenza, and rotavirus have all been shown to exert a herd effect<a href="#accordion">[4].</a> Maintenance of herd immunity in a population for an extended period can lead to the eventual elimination of the disease. So far, only two diseases have been eradicated using herd immunity and vaccination - smallpox and rinderpest in cattle. Researchers are currently working on eradicating poliomyelitis through herd immunity.&nbsp;

&nbsp;

Herd immunity helps protect vulnerable groups in the population and those that cannot receive vaccines. These include newborns, the elderly, cancer patients receiving chemotherapy, and other immunocompromised individuals. However, achieving herd immunity is no easy feat and nor does it always work. Following are the common barriers faced in reaching herd immunity: 
&nbsp;

<ul>
	<li>Vaccine Hesitancy - A refusal to get vaccinated leads to a lower proportion of vaccinated individuals in a community. As a result, the herd immunity threshold is not reached, and the infectious disease can continue to spread. Most people object to vaccines due to safety concerns, religious beliefs, and misinformation regarding the vaccine&#39;s benefits.&nbsp; 
	&nbsp;</li>
	<li>Vaccine Inequality - The unequal distribution of vaccines among low-, middle-, and high-income countries also leads to low vaccination rates in communities.&nbsp; 
	&nbsp;</li>
	<li>Herd Immunity Threshold - Herd immunity can only be achieved if a certain percentage of a population is vaccinated against the disease. This threshold varies depending on the disease. For example, measles requires 95% of the population to be vaccinated while polio requires 80%<a href="#accordion">[5]</a>. 
	&nbsp;</li>
	<li>Mutated Viral Strains - Viruses are constantly mutating and this can give rise to more infectious variants. Moreover, current vaccines may be ineffective against the new variants. Thus, increasing the risk of disease spread. 
	&nbsp;</li>
	<li>Freeloaders - Herd immunity helps protect susceptible individuals, including those who choose not to vaccine themselves. These people are called freeloaders as they benefit from indirect protection but refuse to receive the vaccine. As the proportion of these freeloaders increases in a community, the risk of disease outbreaks also increases due to the loss of herd immunity.&nbsp;&nbsp;</li>
</ul>

&nbsp;

While vaccines are essential to preventing diseases, their efficacy wanes over time. This was evident in a Lancet study that showed decreasing vaccine effectiveness 5-8 months after a second COVID-19 vaccine dose<a href="#reference">6</a>. However, this was more evident in those older than 55 years of age. Moreover, the administration of booster doses restored vaccine effectiveness to levels higher than those seen after the second dose.&nbsp;The emergence of new variants also threatens herd immunity. Boosters such as those against influenza and COVID-19 are updated to include these newer strains. Therefore, boosters are often recommended to help people maintain their level of immunity, especially in the face of new viral mutations.&nbsp;&nbsp;

Conclusion

Although herd immunity can prove beneficial in controlling outbreaks, it does not protect against all vaccine-preventable diseases. For example, since tetanus is spread from the bacteria present in the soil and environment, herd immunity cannot protect you from contracting the disease.&nbsp; 
&nbsp;

Despite the advances in vaccine development and the availability of countless studies on the benefits of vaccines, people remain skeptical about the biological concoction. Community-based education programs can help debunk myths and misconceptions about vaccines and increase uptake, which is a necessary step to achieve herd immunity and controlling disease outbreaks.&nbsp; 
&nbsp;

Nevertheless, vaccines are an important because not only we protect ourselves, but also those around us. Instead of relying on herd immunity, it is best to remain up to date with our vaccinations and educate those around us.&nbsp;

&nbsp;

Key Points

<ul>
	<li>Herd immunity occurs when a proportion of the population becomes immune to a disease. Thus, reducing the spread of the pathogen to others. As a result, susceptible individuals are also protected from the disease. This phenomenon helps protect vulnerable groups in the community that cannot receive vaccines such as the newborns, the elderly, and the immunocompromised individuals.&nbsp;</li>
	<li>Herd immunity can be achieved either through vaccinations or through infection and recovery. However, herd immunity through vaccines is often preferred as it&#39;s more reliable and associated with less risks than natural infection.</li>
	<li>Herd immunity only works against contagious diseases, such as measles, diphtheria, polio, and influenza. Other vaccine-preventable diseases, like tetanus, cannot be controlled by means of herd immunity since they spread through the environment and are not transmitted from person to person.&nbsp;</li>
	<li>The proportion of people required to achieve herd immunity usually varies depending on the disease. This is called the herd immunity threshold.</li>
	<li>Several barriers, such as vaccine hesitancy, the emergence of new disease variants, herd immunity threshold, and an increase in freeloaders can serve as a barrier to achieving herd immunity.</li>
</ul>

&nbsp;

[1] Glatter, K. A. & Finkelman, P., 2021. History of the Plague: An Ancient Pandemic for the Age of COVID-19. The American Journal of Medicine, 134(2), pp. 176-181.

[2] CDC, 2021. History of Smallpox. [Online]

[3] Topley, W. W. C. & Wilson, G. S., 1923. The Spread of Bacterial Infection. The Problem of Herd-Immunity. The Journal of Hygiene, 21(3), pp. 243-249.

[4] Kim, T. H., Johnstone, J. & Loeb, M., 2011. Vaccine herd effect. Scandinavian Journal of Infectious Diseases, 43(9), pp. 683-689.

[5] World Health Organization, 2020. Coronavirus disease (COVID-19): Herd immunity, lockdowns and COVID-19.

[6] Menni, C. et al., 2022. COVID-19 vaccine waning and effectiveness and side-effects of boosters: a prospective community study from the ZOE COVID Study. The Lancet, 22(7), pp. 1002-1010.

Trusted By