How exactly do vaccines work?

In recent weeks there have been multiple measles outbreaks across the United States, most recently in Rockland County, New York. These outbreaks are attributed largely to the anti-vaxxer movement. Let’s take a moment to explore exactly how vaccines work.

Antigens – the uniforms

Imagine every cell in your body wears a uniform to be recognized as not a threat. The uniforms are made of unique molecules. Cells called macrophages are part of the immune system and use the uniforms to recognize whether something in the body is a threat.

Foreign invaders have a unique markers called “antigens”, which sounds the alarm for your immune system to attack. Vaccines are tailored to microbes’ individual antigens to help your body recognize them as threats.

Macrophages carry the microbes to the body’s lymph nodes and destroy the microbes deemed threats, but keep the antigens, and then add them to their “uniforms” so other cells of the immune system can recognize other microbes with the same antigens in the future.

Lymphocytes – The Armies

The body consists of two major types of lymphocytes: T cells and B cells. Let’s picture these cells as massive armies split into units.

The T cells can be offensive and defensive. The offensive T cells, or killer T cell, use chemicals to kill human cells in the body that are infected by the microbes. Killer T cells spot infected cells by recognizing the antigens we previously discussed.

The defensive T cells, also called helper T cells can be viewed as the recon units that signal to the killer T cells when to attack. Helper T cells release chemicals that mobilize killer T cells and other cells of the immune system.

To stick with the military metaphor, B cells can be viewed as the weapons manufacturers that make specific weapons for each unique antigen. The weapons produced by the B cells are called antibodies. Antibodies fight microbes by latching onto their antigens like a “jigsaw puzzle” — if their shapes match, they bind. The immune system stockpiles millions of unique antibodies to prepare for possible invaders. According to the National Health Institute, a teaspoon of blood has approximately 50 million B cells. After a B cell latches on to an antigen, it divides into large B cells and releases more antibodies to destroy the microbe.

Antibodies – the Hunters

Antibodies circulate throughout the body hunting microbes yet to infect cells. When they reach microbes, antibodies attach to the surface, which disables the microbe. Once attached to the microbe, the antibodies send a signal to other cells of the immune system to come consume and destroy the microbe. This is called the Antibody response and is what most vaccines stimulate.


The goal of the immune system is to destroy microbes at a faster rate than they can reproduce. After defeating an infection, B cells and T cells become memory cells. Memory B cells divide and produce more antibodies. Memory T cells divide and grow into large armies. If the same microbes invade the body, the immune system is able to recolonize and destroy them more quickly.

Vaccines are weakened versions of microbes. When vaccines are injected into the body, your immune system reacts and it produces memory cells to prepare it for future invasions.

Find more information on the CDC website

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