Fort Worth, Texas,
10:19 AM

Measles In The Classroom

How community (herd) immunity protects kids from diseases

According to the National Conference of State Legislatures, Texas is among 18 states that allow families to opt out of vaccines for personal or moral beliefs. The Morning News reports that Plano, Fort Worth, Austin and Houston all ranked among the 15 U.S. metro areas with the most such conscientious exemptions for kindergartners. Each had more than 400 kindergartners exempted from vaccines.

Fifteen years ago, about 2,300 students opted out of at least one vaccine. Today, that number has grown to 56,737 kindergarten through 12th grade students.

This has many doctors, including myself, worried about more measles outbreaks in Texas.

"Populations who choose to not follow the recommended vaccine schedule for themselves and for their children are actually setting up the perfect conditions for the diseases they are unvaccinated for to erupt into an outbreak. It is really not a question of whether these outbreaks will occur but when," Jason Terk, M.D., a Cook Children's pediatrician in Keller.

News about vaccine preventable diseases is important for us to share, but it brings up many strong opinions.

Here’s how the debate usually goes:

“Please vaccinate your children.”

“If your child is vaccinated and vaccines are such a good thing, why do you care if my child gets vaccinated?”

Most people don’t have a good answer for it so it tends to be a good trump card.

So why do I care?

There are two reasons.

1. I care about your child. I firmly believe that vaccination is the right thing to do. I vaccinate my children on time and on purpose. I would not want any child to receive less care than I would provide my own children.

2. Vaccines sometimes do not provide complete protection. Most provide protection in the 90-percent plus area (some nearly 100, some lower). Because of this, even a vaccinated child can contract the disease. I will go into this in more detail below, but the more children who are vaccinated for a disease the less likely it is that any child will contract that disease. This occurs through a process known as community, or herd, immunity.

Many people will stop reading right here because they have already decided or have read somewhere that herd immunity is not a real thing. Here are some of the arguments against herd immunity I come across from time to time:

  • It’s not based on a science, but on epidemiology. Epidemiology is the study of the way diseases spread. It is a very complicated field, involves tons of statistics and research and IS science. To say that it is not science is a false comparison.
  • We still have outbreaks even in areas where there are high vaccination rates. This is most definitely true, but does not prove that herd immunity is not real.

How does it work?

Since it's most timely, let’s use measles as an example. First, you need to know some things about measles…

Measles has an attack rate of a susceptible individual at 75 percent. This means that 75 percent of people exposed to measles who are not protected will contract the disease. I’ll use 70 percent to keep my numbers round and err on the side of people who would disagree with me.

Measles vaccination has a 95-100 percent protection rate. Again, I will use 95 percent so that I am not cherry picking the best results to prove my point.

There are two scenarios below. The first scenario has a case of measles in a classroom where everyone else is vaccinated. The second scenario is a case of measles in a class with one child who is not vaccinated.

Scenario No.1:

Scenario No. 2:

In scenario No. 1, all the children are vaccinated which means they have a 5 percent chance of catching measles. If that child goes to another class or event where all children are vaccinated, each of those children have much less than a 5 percent chance because the child doesn’t likely have the disease and they only have a 5 percent chance of catching the disease even if he did.

In scenario No. 2, one child in the classroom is unvaccinated. He thus has a 75 percent chance of catching the disease. He’s going to go to other locations with other children, even if those children are all vaccinated, we have potentially opened up a whole second circle of exposed children. Not to mention that the children in the first class have now potentially been exposed twice.

So, in scenario No. 2:

  • If I gave you a choice, would you want your child in group A or B?
  • Does it matter if your child is vaccinated or not?
  • What if you also have a baby in your house who cannot be vaccinated?
  • What if you child is in class B, but has a disease for which they cannot receive the MMR vaccine?

The answer is no, none of these things matter. Logically, we should all want our child in room A because it decreases the odds of our child being exposed. Is it 100 percent? No, but it doesn’t matter. Are you more likely to be angry about a measles outbreak if your child cannot be vaccinated? Yes, and I understand that.

For one last thought, consider this … a  study in Pediatrics described geographic clusters of people who choose not to vaccinate at all or to under-vaccinate their children. I suspect that is true across our area as well, but I also suspect that there is clustering according to other factors as well: socioeconomic status, church/religious affiliation, etc. Populations where there are multiple families who choose not to vaccinate would be particularly susceptible in an outbreak situation. Let’s pray we don’t get there.

This is herd immunity and why the question, “If your child is vaccinated and they are such a good thing, why do you care if my child gets vaccinated?” doesn’t end the conversation.

Get to know Justin Smith, M.D.

Justin Smith, M.D., is a pediatrician in Trophy Club  and the Medical Advisor for Digital Health for Cook Children's in Fort Worth, Texas. Dr. Smith is an experienced keynote speaker for a variety of topics including pediatric/parenting topics, healthcare social media and physician leadership. If you are interested in having Dr. Smith present to your conference or meeting, please contact him at

He has an active community on both Facebook and Twitter as @TheDocSmitty and writes weekly for Cook Children's He believes that strategic use of social media and technology by pediatricians to connect with families can deepen their relationship and provide a new level of convenience for both of their busy lifestyles. Dr. Smith’s innovative pediatric clinic, a pediatric clinic “designed by you,” open now. Click to learn more. To make an appointment, call 817-347-8100.


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So these families have the right to not vaccinate their children....what about the people who do vaccinate their children - don't they have the right to not have their children exposed to kids who are not vaccinated. Why is it that those who go "against the grain" are the only ones who seem to have RIGHTS. If you don't want to vaccinate your child and have that right...then okay. But don't send them to the school where my child/grandchild is.