Herd immunity works by controlling the spread of a disease within a population when a large section of people become immune to the disease either through vaccination or immunity developed from a previous infection. It is also known as community immunity. When the immunity bar is reached, most individuals get protected from infection because the disease doesn’t spread as rapidly as before. It protects those who are immune and people who have not acquired resistance.

Importance of herd immunity
Herd immunity safeguards a community from a contagious disease. It happens when a percentage of the population becomes resistant to an infection, thereby lowering the chances of a spread. Unvaccinated people will also receive protection because other people around them are immune. These immune people act as buffers between them and an infected person. Once herd immunity is achieved to some extent, the disease can eventually be eliminated. Due to this phenomenon, many individuals who are not even vaccinated are offered protection because the disease gets less opportunity to spread within the community. However, a certain group cannot be vaccinated and are exposed to the threat of disease, including babies, pregnant women, breastfeeding mothers, or a patient receiving chemotherapy or organ transplants.

When most people are vaccinated, everyone receives some protection from the spread of diseases. The proportion of a community that needs to be immune against disease to achieve herd immunity varies depending on the type of infection.

Besides getting immunized, another way herd immunity is achieved is when a significant portion of the community has been infected with the disease and recovered from it. Natural immunity happens when a person’s immune system develops antibodies against the pathogens causing the condition.

Who receives protection in herd immunity?
Herd immunity offers protection to people who are not immune to a particular disease and fall into the following categories-

• People who never had the disease
• People who can’t get vaccinated
• People who have a weak immune system

Challenges associated with herd immunity
Greater population resistance is needed to ensure herd immunity if the disease is highly infectious. For example, since measles is contagious, one person with this disease can infect up to 18 more people. Hence, around 95% of people should be immune to the disease to protect a wider group. It is also believed that community immunity can be achieved through vaccination projects. Sometimes, even with immunization, herd immunity can take a long time to develop because some viruses, like seasonal flu, mutate frequently and evade the body’s immune system. So, in such a case, immunity doesn’t last long. It is the reason why the flu shot is necessary every year.

Risks related to herd immunity
Many countries have successfully induced herd immunity against various health conditions through mass vaccination projects. Community immunity helps protect people who are immune deficient or whose immune system is weakened due to health reasons.

When doesn’t herd immunity work?
A major shortcoming is that many people, including unvaccinated individuals, move freely in the same neighborhood when herd immunity is established. Therefore, chances are there for many unvaccinated people to come closer. Once the number of immunized people in the population drops below the herd immunity threshold, the contagious disease can spread quickly throughout the community. It can put everyone at risk of contracting the disease. The herd immunity threshold refers to the proportion of a community that must become immune to a contagious disease so that other people who received immunity are less likely to interact with an affected individual and become infected.

Example
Smallpox is one of the biggest examples of a disease eradicated through herd immunity.

Besides getting vaccinated against the infection, there are various other ways to ensure the disease does not spread within a community. It includes wearing masks both indoors and outdoors, maintaining a safe distance from strangers, avoiding large social gatherings, washing hands often, and seeking a healthcare provider’s attention when feeling sick.

Herd immunity appears when a large part of a population living in an area becomes immune to a specific disease. While not every single person can be safeguarded, the group as a whole is offered protection. It acts as a barrier to save those with weak immune systems, small babies, and those who can’t resist the disease alone. Herd immunity is achieved when a maximum number of people in a group get vaccinated or receive immunity against a health condition. It is the best way to help prevent community spread.