The Relationship Between Vaccines and Herd Immunity

April 9, 2021

Vaccinations are crucial in the fight against infections and viral spreads. However, when not everyone in a population can access vaccination, herd immunity becomes vital in ensuring protection.

Since the outbreak of COVID-19, the idea of "herd immunity" has entered the public vernacular as a way to reduce the spread of the virus.

So, what exactly is the herd immunity theory? Herd immunity, and its relationship with vaccines, is important to understanding the prevention of the spread of infections and diseases.

What is Herd Immunity?

Herd immunity describes a situation in which a large part of a population is immune to a particular disease due to vaccination or previously contracting the illness and developing anti-bodies. This indirectly also helps ensure the protection of the remaining population, and offers a higher chance of combating and reducing transmission.

In many cases, herd immunity ensures that while not everyone is immune to the disease, everyone can enjoy protection from it. The higher the number of immune people in a population results in a lower risk of contracting the disease or virus for everyone.

Why is Herd Immunity Important?

While it may be unrealistic to assume every individual in a population is able to get vaccinated, those outstanding individuals will then rely on herd immunity to avoid contracting a virus.

Reasons for not receiving a vaccination include:

  • People with weak immune systems

  • People that are going through chemotherapy treatments

  • Newborn babies and elderly people

  • People living with HIV

  • Those who refuse vaccination

In every community, you will find individuals who fall under the above categories, making herd immunity that much more important. These people then depend on others getting vaccinated in order to be indirectly protected by them.

Vaccine Herd Immunity Explained: How are Vaccinations Related to Herd Immunity?

Herd immunity is reliant on immunity from a disease. Immunity can be achieved in one of two ways: prior infection or vaccination. In many cases, relying on prior infection is an unrealistic—and even dangerous—way to reach herd immunity.

That’s why vaccines are essential in the fight to establish herd immunity. Illnesses like polio and chickenpox are now very rare due to the impact of vaccine herd immunity.

Wide-spread vaccination makes large swaths of the population immune to a given disease, dramatically reducing the potential to transmit it to others, and ultimately preventing an outbreak from happening.

In cases where vaccinations cannot get to every person in the population, herd immunity makes it difficult for the disease to spread from person to person, protecting those that cannot access vaccinations.

The specifics of herd immunity will often depend on the nature of the disease or virus in circulation. Certain diseases such as Ebola, influenza, and COVID-19 spread easily and swiftly. Other diseases require more unique circumstances for contraction.

Depending on the nature and level of contagion of a given disease, public health professionals will determine the total percentage of people in a population that must receive the vaccine to help facilitate herd immunity.

Herd Immunity Examples and Thresholds

A large percentage of the population must be immune to the virus in some way in order to reach herd immunity.

This threshold will vary depending on the disease—measles herd immunity requires 95% of the population to be immune, while polio requires 80%.

In the case of COVID-19, health professionals estimate 70-90% of the population must be immune in order to achieve herd immunity.

Vaccines and Herd Immunity: A Way Forward

Vaccinations play a crucial role in achieving herd immunity in any population. For example, in 2000, measles was declared defeated in the U.S. However in 2019, a surge of new cases was recorded. This occurred as a result of the stalled vaccination rates, showing the importance of vaccinations and their impact on herd immunity.

It is impossible to discuss the possibilities of achieving herd immunity without talking about the novel coronavirus. For over a year, COVID-19 has swept through the world, crippling economies, enforcing lockdowns, and sadly, taking lives along with it.

With concerns being raised over a new wave of the virus, health experts are working tirelessly towards solutions and vaccination protocols in order to stop the spread.

The possibility and requirements that come along with achieving herd immunity have also been discussed. The CDC and other experts are continuously studying herd immunity and the total percentage of people who will require vaccinations to achieve it.

Since not everyone in a population will get the vaccine, herd immunity will be a crucial factor in slowing or even ending the pandemic. It can be achieved if the highest possible number of people get the recommended vaccine.


The Columbian Mailman School of Public Health has been a strong voice and advocate for public health research and education. With numerous publications on issues surrounding public health, community collaboration, and health research, we aim to educate and inform the public on public health and safety. Visit our program pages to learn more about our public health degree programs.