Vaccine Scares and Behavior Theory: How Herd Immunity Affects Vaccination Rates


Home / Vaccine Scares and Behavior Theory: How Herd Immunity Affects Vaccination Rates

This graphic illustrates the contrast between a community with no herd immunity (top) and a community with herd immunity (bottom) – Image courtesy of NIAID

What is Herd Immunity?

One of the main focuses of the study was the concept of ‘herd immunity.’  Herd immunity occurs when a large group of people are all vaccinated against a disease, which then limits the spread of the disease due to a lack of potential carriers or victims. Herd immunity means that even people who are not vaccinated may not get a particular disease because the majority of people are vaccinated, and therefore are not carrying around the virus to infect others. Dr. Bauch’s study found that, because of herd immunity, those who were not vaccinated had no incentive to become vaccinated. This mindset allows for more opportunities for diseases to spread and can result in severe outbreaks.

I asked Dr. Bauch about his recommendations to people who chose not to vaccinate, and instead rely on the theory of herd immunity and he replied:

“There have been numerous studies showing that even when disease is low, you are still at greater risk from the disease than from the vaccine.  This is because even if a disease has been eliminated in a population, there is a chance you could get infected by someone who brings the disease back from a country where it has not been eliminated.  Because modern vaccines are so safe, the small chance of getting very sick through contacting someone who has imported the disease from elsewhere still outweighs the small risk of the vaccine.”

I also asked Dr. Bauch about his recommendations to medical and public health professionals who work to keep the population healthy. He replied:

“These professionals should emphasize that even if there is not much disease around, we need to continue vaccinating until the disease is completely eliminated.  The consequences of a few individuals not vaccinating are severe because if enough individuals stop vaccinating, the disease will come back and will adversely affect the health of many individuals, and it will push back elimination efforts by many years.  Hence, vaccinating is essentially a team effort.  They should also emphasize the risk of getting the infection through contact with individuals from countries where the infection has not been eliminated, hence even if the disease is rare locally, the vaccine can protect them against infection from international sources.”

Concluding our interview, I asked Dr. Bauch if he had any final thoughts or comments and he replied:

“This research shows that mathematical models could have a valuable role to play in helping public health respond to vaccine scares.  We hope to develop this capacity further in the coming years.”

Why is the Study of Herd Immunity and Behavior Important?

Dr. Bauch’s study provides a great deal of insight for medical and public health professionals who strive to keep the population healthy. This study also demonstrates the importance of understanding people’s behavior so that health professionals can better focus their efforts in protecting large populations.


Bauch, C.T., Bhattacharyya, S. Evolutionary Game Theory and Social Learning Can Determine How Vaccine Scares Unfold. (2012). PLoS Comput Biol 8(4): e1002452. doi:10.1371/journal.pcbi.1002452. Accessed April 5, 2012. 

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