“If your vaccines are so effective, why are you so worried that I don’t get mine? Doesn’t that mean that the vaccines don’t work?”

Every time this is posted online, an angel gut checks a medical student. This fairly common misunderstanding is the bane of the American public health community, right up there with abstinence only education and chili cheese fries. And while arguing with anti-vaxxers online is generally not the most productive use of a person’s time, it is important that an educated public understand the basics behind the concept of “herd immunity” and why everyone who can medically receive vaccinations should do so.

Vaccination is the process of getting the body’s immune system prepared for a specific contagious disease. There are several criteria for determining whether or not a vaccine is effective, including safety and possible side effects, whether or not it induces the correct neutralizing antibody for the specific disease, whether or not it gives sustained protection, and other practical considerations like costs per dose and ease of administration. When vaccines are administered, white blood cells in the body called B-cells are activated to reproduce. They produce antibodies for whatever disease causing substance has been introduced to them, whether that substance was a bacterial protein or a weakened or dead virus. Some of these B-cells live on in the blood stream for years as memory B-cells, waiting for the activating signal to start reproducing and making more of the specific antibody that was made the last time the foreign invading material was introduced. When the disease causing agent that someone was vaccinated for is introduced to the body after a successful vaccination, these cells and antibodies will form an immune response, preventing the disease from taking hold in the body. While no vaccine is always perfect, they are about 95-99% effective at achieving the desired effect. I highly recommend Kuby’s Immunology (Sixth Edition) and Janeway’s Immunobiology (Eighth Edition) for anyone who wants to know more about the intricate processes of the body’s immune responses.

If enough people within a population get vaccinated and become immune, then the disease causing agent will not take root because it will be killed by a person’s immune system before it has a chance to reproduce in their body and spread to a new host. The more people who are vaccinated, the less likely it is that a person who is carrying the disease to spread it to anyone else, and thus the disease cannot spread through the population. This is how diseases like polio were largely eliminated from the developed world. This critical point in the population where so many people are immune to a disease that the disease cannot spread is herd immunity.

If a person does not receive a vaccination, they could still be carrying the disease even if they are not showing symptoms of it. They could be physically healthy and their body could be fighting off the disease without them showing symptoms, but the disease causing virus or bacteria is still able to live, reproduce, and spread. While they don’t get sick themselves, they can become another carrier of the disease. This becomes a problem when people who are carrying the disease are exposed to someone who isn’t in perfect health.

People who are already having health problems are in the most danger from communicable diseases that would otherwise be prevented by vaccinations. People with autoimmune diseases can’t receive certain shots. Newborn babies who aren’t old enough to be vaccinated, the elderly, people with cardiopulmonary diseases or cancer, and a myriad of other chronically ill people are all potential victims of a disease outbreak. This is why most disease outbreaks that would typically be prevented by vaccines occur in places with a lot of kids or sick people, like schools or hospitals. Disneyland was recently the site of a measles outbreak, where viral genetic analysis has shown that the virus was most likely brought into the park by a person visiting from overseas and spread rapidly through children, most of whom were not vaccinated.

The point of mass public immunizations is to prevent diseases from spreading, allowing the healthy to remain healthy and allowing those in less than perfect health to not be made even more ill by something preventable. We give children their vaccines to protect them from diseases. As adults, we take vaccines to not only protect ourselves but to protect those around us from diseases that we might accidentally spread to them. I stay up to date on my vaccines because I don’t want to put those less fortunate at risk or get sick myself. Whether it be my friend from grad school with multiple sclerosis, my student with Sjogren’s syndrome, or any passing person on the street, other people deserve the courtesy of public safety from preventable communicable diseases.

Here’s a really cool simulator someone made to demonstration the efficacy of herd immunity, you know, in case all this scientific data isn’t good enough for you.


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