Vaccines trick the body to build a defense against bacteria, diseases and viruses. Once introduced into the system, the body’s white blood cells attack and destroy these pathogens. From then on, these little soldiers stand constant watch. On detection, they instantly move to destroy the disease before it gains a foothold. A vaccine is a pretender, a double agent of sorts, that helps protect the body.

Doctors use one of five vaccines types to help prevent disease:

• Attenuated vaccines contain a weakened version of the living virus such as those used for measles, mumps, rubella and varicella viruses like chickenpox.
• Inactivated vaccines help the body’s immune system fight the disease by adding a killed version of the vaccine to the body, like polio vaccines.
• Toxoid vaccines, like diphtheria and tetanus, contain weakened toxins to prevent diseases caused by these bodily enemies.
• Subunit vaccines include the crucial antigens of the virus or bacteria to help build the body’s immunity against diseases like whooping cough.
• Conjugate vaccines help a child’s still-developing immune system to hunt antigens that try to hide behind a sugarlike coating to trick the body.

Vaccines and immunizations are not the same. A vaccine poses as a disease to trick the body into building antibodies, just like it would after recovery from a virulent disease. An immunization represents the physical act of inoculation with the vaccine. For parents, an immunization schedule details the age and dates when children should receive specific vaccinations.

Inside the bloodstream, antigen-presenting cells, the soldiers on guard-watch, float around as they look for invaders. Once a vaccine enters the body, the APCs capture it, ingest it, tear it up and wear a piece of the antigen on their outer surfaces.

These cells head back to headquarters where immune cells cluster, like inside the lymph nodes, to share the news about the disease. Certain naïve T- and B-cells, cells not previously exposed to the disease, recognize the invader as foreign and immediately sound the alarm to rouse the troops.

After the cells activate, some of the naïve B-cells develop into plasma B-cells. T-cells start producing Y-shaped proteins – antibodies – that the immune system releases each second. Each of these antibodies tightly attaches to the targeted antigen, much like a key enters a lock, to keep the disease from entering the cells of the body.

The body’s immunity army now recognizes these antigens as the enemy and targets them for destruction. In vaccines with weakened versions of the disease, the antigens pass into the cells where special-op forces, the killer T-cells, immediately eliminate them. From that moment on, B-cells, T-helper and T-killer cells commit the disease to memory, which allows them to recognize and destroy the real disease should it enter the body in the future.

A vaccine essentially allows the body’s immunity army to practice on the pathogen, making the body stronger and helping it respond faster than it normally would if it were first encountering the disease. Researchers and scientists call this the “secondary response” to the pathogen, which results in the creation of more antibodies and memory cells to help identify the enemy in the future.

The job of the body’s immunity army is threefold: hunt for dead cells to remove them from the body, destroy and eliminate abnormal cells and protect the body from foreign invaders like parasites, bacteria and viruses.

The immune system provides physical and chemical barriers in an innate response, by nonspecific resistance – the body’s innate system that fights disease – and through specific resistance, like an acquired immunity obtained through a vaccine.

Physical and chemical responses refer to the actions of the skin, mucous membranes, and hair within the nostrils and cilia within the lungs that trap pollutants and disease, as well as vomiting, urination and defecation to remove toxins and waste. Chemical responses include the natural chemicals within the body such as stomach acid and skin acidity, which all fight disease and bacteria.

Vaccines help not only an individual body fight against disease, they also help protect a community, known as herd immunity. Disease outbreaks occur less often when more of the population receives vaccines. As the number of vaccinated people grows, the defense effect of herd immunity also increases. Those who cannot receive a vaccination because of weak immune systems or allergies benefit from herd immunity when the vaccination rate ranges from 80 to 95 percent of the entire community.

No vaccine is 100 percent safe, says the Children’s Hospital of Philadelphia. If you think about it logically, vaccines present the body with a modified version of the disease, which can lead to pain, redness or tenderness at the inoculation site and a muted version or reaction to the disease. For example, some of the original whooping cough vaccines sometimes caused high fevers and seizures. Though frightening, these symptoms typically didn’t result in permanent damage.

Researchers, scientists and doctors posit that the protections received from vaccines far outweigh the consequences of living without them. Many people believe that letting the body’s natural immune system respond by itself without help from a vaccine is the preferred course of action.

But this doesn’t always work when you think of all the children paralyzed during the polio outbreak in the 1940s and 1950s. While those with weak immune systems or allergies to components within a vaccine may not benefit from a direct inoculation, they do benefit from herd immunity.

When people stop their children from receiving vaccines, they affect more than just their immediate families. The lack of vaccine immunization – besides a disease's debilitating effects – can cause an outbreak that spreads to all the vulnerable people of a community, and eventually, the world.