Why Worry About the Unvaccinated?
Apr 12, 2011

Time and again, we hear this from parents who choose not to vaccinate their children…

“If your child is vaccinated, why are you worried about them catching anything from my child?”

This is a common response from parents when it is suggested that a purposely unvaccinated child poses a threat to others.

One thing that many parents may not understand is that while vaccinations are highly effective and greatly decrease the chance of getting a preventable disease, according to the CDC, depending on the vaccine, about 1% to 5% who are vaccinated fail to develop immunity. The CDC states, “It isn’t very common, but it can happen…If these children are exposed to that disease, they could get sick. Sometimes giving an additional vaccine dose will stimulate an immune response in a child who didn’t respond to 1 dose. For example, a single dose of measles vaccine protects about 95% of children, but after 2 doses, almost 100% are immune.”

This explains why, during an outbreak of a vaccine-preventable disease like measles, an unvaccinated child can increase the risk of disease for everyone that may be exposed, even if the people who have been vaccinated vastly outnumber those who have not.  It is not uncommon for a small portion of the vaccinated population to be infected. However, that does not prove that vaccinations are not effective.  To truly understand the risks, you need to know more than just the number of vaccinated vs. unvaccinated who have become infected.

This example from CDC’s “Six Common Misconceptions About Immunization”, helps further explain this concept:

“In a high school of 1,000 students, none has ever had measles. All but 5 of the students have had two doses of measles vaccine, and so are fully immunized. The entire student body is exposed to measles, and every susceptible student becomes infected. The 5 unvaccinated students will be infected, of course. But of the 995 who have been vaccinated, we would expect several not to respond to the vaccine. The efficacy rate for two doses of measles vaccine can be higher than 99%. In this class, 7 students do not respond, and they, too, become infected. Therefore 7 of 12, or about 58%, of the cases occur in students who have been fully vaccinated.

As you can see, this doesn’t prove the vaccine didn’t work – only that most of the children in the class had been vaccinated, so those who were vaccinated and did not respond outnumbered those who had not been vaccinated. Looking at it another way, 100% of the children who had not been vaccinated got measles, compared with less than 1% of those who had been vaccinated. Measles vaccine protected most of the class; if nobody in the class had been vaccinated, there would probably have been 1,000 cases of measles.”

When enough people are vaccinated against a certain disease, the germs can’t travel as easily from person to person and the entire community is less likely to get the disease. This concept is known as “herd immunity” or “community immunity”. Community immunity protects everyone, and it is especially important for people who are vulnerable to diseases, but who can’t be vaccinated. This includes children too young to be fully vaccinated, people with serious allergies against certain vaccine ingredients, and people with weakened or failing immune systems (e.g., people with cancer/going through cancer treatments, people with HIV/AIDS, people with type 1 diabetes, or people with other health conditions.)

Community immunity is also important for the very small group of people who don’t have a strong immune response to vaccines. These people who cannot get vaccines or who aren’t protected from vaccines depend on a high level of immunization in their schools and/or their communities to help protect them against dangerous, and potentially deadly diseases.

Each vaccine-preventable disease requires a certain percentage of people in a community be vaccinated in order to prevent the disease’s spread. This is called the “Community Protection Threshold”. The exact percentage depends largely upon how easily a disease can spread from person to person.





When we consider this in relation to what is currently happening in our own communities today, we see why there is reason for the vaccinated to be concerned.  Following are some examples:

According to the Minnesota Department of Health, a 2011 measles outbreak was caused in part by former doctor and medical researcher Andrew Wakefield’s influential but fraudulent study suggesting a connection between child vaccination and autism. Due to his influence, many children in a Somali community there have chosen not to have their children immunized.  Unfortunately, one of these unvaccinated children,  was identified with measles after returning from a trip to Kenya. Currently, 15 cases have since been identified, five of which were too young to have received the vaccine, six were of age but were not vaccinated, one was vaccinated and three have unknown vaccine status, with a total of eight hospitalizations having been reported so far. Read updated information about this 2011 measles outbreak.

A small private school in Roanoke, VA, was closed due to an outbreak of pertussis (more commonly known as whooping cough) in 2011.  The school, which does not require students to be vaccinated, has reported 30 confirmed cases; 23 of which have been among the school’s 45 students, the others among staff.  Dr. Molly O’Dell, director of the New River Health District, explained that the infected children were not vaccinated, while the adults infected were never revaccinated with a booster shot.  Unfortunately, many adults do not realize that their immunity to pertussis wanes over time, and that a booster shot is suggested for continued immunity.  According to the Virginia Dept. of Health, a total of 399 pertussis cases were reported in 2011.

In Utah, a confirmed case of measles first appeared in an unvaccinated teen who returned from a trip to Europe.  Since then, three other cases have been confirmed, none of which were vaccinated.  Now, with six other suspected cases and a trail of possible exposure, it appears that the measles may have spread to four different schools.  Gary Edwards, executive director of the Salt Lake Valley Health Department explained that “The vaccine is very effective against this illness,” which is why children who have not been adequately vaccinated will be temporarily excluded from school in order to contain any further spread of the disease.  Read updated information about the two measles outbreaks in Utah in 2011.

In each of these examples above, it is completely possible that some vaccinated children may become infected. However, it was the unvaccinated children who introduced the disease into these communities. These examples of cases and outbreaks of vaccine-preventable diseases are just a few of the many that occur all over the country at any given time. These examples also serve to answer why a vaccinated person might be concerned about getting a disease from the relatively small unvaccinated segment of the population.

Perhaps this video by Shane Killion, which was brought to our attention by Gary Attarian on our Vaccinate Your Family Facebook page, can further help to illustrate herd immunity by providing a simulation.  It can be effective in helping people understand how vaccine refusal can impact an entire community, even if that community is mostly vaccinated.  The dots on the screen  represent either vaccinated or unvaccinated people.  The video then uses percentages to demonstrate the impact of a disease and the public health consequences of a person who refuses vaccinations.

Hopefully, as parents gain a better understanding of vaccinations, they will also come to understand why the vaccinated population might be concerned about vaccine refusal.

Unfortunately, public health is just that – PUBLIC. And one person’s vaccination decisions impacts the health of many others, whether they realize it or not.

Learn more about vaccine science and how vaccines work on the Vaccinate Your Family website.

Learn about current vaccine-preventable disease cases and outbreaks in the U.S.

Portions of this 2011 blog post were updated in February 2018 by Vaccinate Your Family.

Related Posts

Vaccinate Your Family was pleased to host Dr. Laura Riley of NewYork-Presbyterian Hospital and Weill Cornell Medicine, in collaboration with American College of Obstetricians and Gynecologists – ACOG, as she answered questions about COVID-19 and other...

Not many people know more about how to approach talking to friends and family about being vaccinated than Riki. She’s a physician liaison for the liver team at Houston Methodist Hospital and a pro-vaccine advocate. But most importantly, she’s a heart mom.   Riki’s daughter, Juliana, was born in heart...

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.