Pediatrician Rhea Boyd defines for us the meaning of herd immunity, which is also known as “community immunity”:

We often say it takes a village to raise a child, but the truth is, it takes a herd.

Herd immunity is the protection from contagious disease that an individual benefits from as a result of living in a community where a critical number of people are vaccinated. That means, individuals who live in communities with high vaccination rates are effectively protected from vaccine-preventable infectious diseases​, even if they themselves are not able to receive certain immunizations.  The National Institute of Allergy and Infectious Diseases created this graphic [above] to show just how herd immunity works.


Dr. Boyd explains why immunizing the maximum numbers of members of any given community against deadly vaccine-preventable diseases is so important:

Herd immunity is important because it uniquely protects the most vulnerable members of our communities, including infants, pregnant women and other individuals whose immune systems cannot combat certain harmful or deadly infections or who aren’t eligible to receive certain vaccines. It also prevents outbreaks and epidemics of preventable, infectious disease. 

Many pediatricians consider vaccination one of the earliest and most important decisions parents can make for their children, starting with the Hepatitis B vaccine babies usually receive in the hospital nursery. But as the image shows, while the impact of vaccinating babies affects their individual health, it also has a positive effect on the health of the entire community.


The herd gets larger as the modern world gets smaller and more connected, say Emily Willingham and Laura Helft:

But today, our chains of connection traverse the globe—reaching across oceans and over mountain ranges, pervading immense cities and remote villages—linking us all into one vast, interactive human herd. Almost no one anymore lives in isolation from such connections.


Willingham and Helft examine one previously common and occasionally fatal childhood disease that is thankfully quite rare today, offering insight into the importance of herd immunity:

After the chicken pox vaccine debuted in the United States in 1995, deaths rates from chicken pox dropped by as much as 97%. Significantly, even though the vaccine is not administered to infants, no infants died from chicken pox in the United States between 2004 and 2007. These tiniest, most vulnerable links in the chain of human connections avoided exposure thanks to herd immunity.


This brief video from Chain of Protection demonstrates simply how herd immunity works:


*** On January 22, 2018, Pediatric Alliance and some of our pediatric colleagues from around the United States began participating in an 8-week AAP-sponsored immunization advocacy campaign on social media. Please follow all our social media posts during this project on Facebook and Twitter.


(Back pat: Tamalpais Pediatrics)