You’ve probably heard the phrase “herd immunity” used a lot over the past few years, especially in relation to the COVID-19 pandemic. But what is herd immunity, how do we achieve it, and can it really help us fight COVID-19? Let’s take a look.

Herd immunity, (also called community immunity, or population immunity) is defined as a kind of indirect protection from some infectious diseases. This kind of protection helps both individuals and large communities.

It is said to occur when a large percentage of people in a community become immune to the disease. This happens either through the natural development of antibodies after being infected with a disease or through vaccination. 

When this happens, it is said to reduce the spread of the disease. This is because once most of the population is immunized, they do not spread the disease anymore. When this happens, it stops or slows the spread of disease which protects people who aren’t vaccinated, or who have weak immune systems.

How do we achieve herd immunity?

There are two main ways for any community to achieve herd immunity:

1. When many people contract the disease and build an immune response to it (natural immunity).

2. When a significant number of people are vaccinated against the disease, and thus achieve immunity.

However, the WHO notes that it is better to achieve herd immunity through vaccination, “not by allowing a disease to spread through any segment of the population, as this would result in unnecessary cases and deaths.” Unlike this natural immunity, vaccination allows people to develop antibodies to a disease without falling ill. It also allows doctors and scientists to periodically boost this immunity (with vaccine boosters) as required. 

However it is achieved, herd immunity depends on how contagious a disease is. Diseases that spread easily, like measles, require a higher number of people to be immune to the illness.

For example, in the case of measles, 95% of the population needs to be immune to the disease for the remaining 5% to be reasonably protected from infection. On the other hand, for polio, about 80% of the population needs to be immune.

Does herd immunity work?

While herd immunity can help stop the spread of many infectious diseases, it does not guarantee any community protection against the disease if vaccinations are not also used. This is because a disease can change and evolve more quickly than people develop immunity. Therefore, for most people, natural herd immunity is not a real alternative to getting vaccinated.

However, when herd immunity is achieved through a combination of vaccinations and natural immunity, it could help prevent widespread disease for some illnesses. 

For example, in Norway, communities successfully developed partial herd immunity to the H1N1 virus (which caused the Swine Flu Pandemic) using this mixture of vaccinations and natural immunity.

However, for some diseases which cannot be transmitted from person to person but from environmental causes (such as tetanus), herd immunity doesn’t work. In such cases, if there is a vaccine (like the tetanus vaccine), that is the only protection.

As we have seen, the only way to achieve herd immunity is either through vaccination or exposing people to a disease. However, since COVID-19 is so deadly, herd immunity should only be achieved through widespread vaccination, not by allowing the spread of a disease that could result in unnecessary illness and death. 

Scientists still do not know what percentage of people need to be immune to COVID-19 to achieve herd immunity. 

Therefore, the main way to fight the disease, save lives, and achieve immunity is through vaccines. Once the majority of the population is vaccinated (including healthy adults, teens, and older children), they will be less likely to contract the virus and transmit it. This will help to provide herd immunity for those who cannot get the vaccine, or develop a natural immunity to the virus.

Herd immunity refers to when a large percentage of people in a community have become immune to a specific infectious disease that the spread of the disease gets significantly slowed down. This is usually achieved through vaccination and natural immunity. 

It can certainly be a great help to prevent widespread disease within a country, such as the COVID-19 pandemic. However, since people’s natural immunity against a disease can change or end very quickly, for most people the best way to achieve proper protection against a disease such as COVID-19 is vaccination.