What Are Vaccines?

A vaccine is a biological substance designed to protect humans from infections caused by bacteria and viruses. Vaccines are also called immunizations because they take advantage of our natural immune system’s ability to prevent infectious illness. To understand how vaccines work, we need to consider how our immune system protects us from infections.

The Immune System

The immune system is a 24-hour machine equipped to manage attacks from invaders to prevent or inhibit infections. It is made up of organs, tissues, and several types of cells that work together to protect the body. The immune cells must be able to determine which cells or proteins are normally in the body and which ones are foreign. Bacterial and viral cells have markers called antigens. Antigens are capable of inducing an immune response in the body. Each type of bacteria or virus has different antigens.

First, in the presence of foreign cells or proteins that may cause danger, special immune cells called lymphocytes, become active. They take steps against the antigen and its owner, either by unleashing a direct assault on the invader or discharging antibodies to do the job. Think of it as a lock and key system. Specific antibodies take out specific antigens.

After an infection, sometimes the antibodies remain in the blood and will begin to fight the infection right away if you are exposed to it again. At other times they do not. However, the next time the antigen is identified, the body recognizes them (memory) and begins to make antibodies against it. Common symptoms, like a sore throat or fever, may be present until the immune system catches up with the invaders. A fever is one way the body fights invaders.

The immune system, while efficient, is specific. It is designed to promote future or long-term immunity to individual organisms. One example is the seasonal flu. Have you ever wondered why you or someone else gets the flu every year, even when you have had it before? The answer is that there are many different strains of the influenza virus that get passed around each season. These different strains all have different antigens. Being immune to last year’s flu strain may protect you for the duration of the season, but it will be of little use when next year’s strains come around.

That's why vaccines are useful and important. They are designed to create defenses against specific diseases before you even get them and help you stay healthy.

How Vaccines Fit In

The concept behind vaccines is to stimulate an antibody memory response without producing an actual illness. When this happens, you get the immunity without getting sick. A vaccine must contain at least one antigen from the bacteria or virus in order to get a response.

There are several ways an antigen can be used:

• Attenuated live viruses—Weakened forms of a live virus. They do not cause illness, but will create an immune response. Examples include the MMR (measles, mumps, rubella) and chickenpox vaccines.
• Inactivated viruses—A version of the virus that has been killed. Although the virus is dead, antibodies will still be produced. Examples include the polio vaccine.
• Recombinant—Viruses are made in a lab through genetic engineering. This way, a specific gene can be reproduced. The human papillomavirus (HPV) has several strains. The HPV vaccine can be tailored to protect against strains that cause cervical cancer.
• Conjugate—Bacteria and virus antigens may have a polysaccharide coating, a sugar-like substance to protect it. Conjugate vaccines work around the disguise to recognize the bacteria. The Hib vaccine is an example of a conjugate.
• Subunit—Uses only the antigens that stimulate an immune response. The flu shot is a subunit vaccine.
• Toxiod—Inactivated versions of bacterial toxins are used to make the immunity. Examples include the tetanus and diphtheria vaccines.

The presence of a vaccine in the body causes the immune system to produce antibodies against the invading antigens. Usually, it takes more than one vaccine to attain a full response. Most are done in a series of vaccines that are given at specific intervals of time. Some, such as tetanus, may need to redone periodically to maintain immunity (a booster).

Reduction in immunity over time can cause outbreaks of disease in a group or community of people who no longer have immunity. This happens periodically with mumps outbreaks on college campuses or in cases of pertussis (whooping cough) in adults. Outbreaks can also occur because of lapses in booster doses or in areas where vaccination rates are low. Increases in the rates of whooping cough, measles, and mumps result from these lapses.

Vaccines can be:

• Injected (most common)—a needle is inserted into a muscle or just under the skin
• Oral—taken by mouth
• Intranasal—inhaled through the nose

Vaccines to Prevent Other Diseases

All vaccines are designed to target infections. However, two commonly recommended vaccines have the added benefit of protecting against cancer:

• Hepatitis B—Because it is a cause of liver cancer and alcoholic cirrhosis, a hepatitis B vaccine can help protect you against these liver diseases. There is also a vaccine available for hepatitis A.
• HPV—The leading cause of cervical cancer and the precancerous cervical dysplasia in females. In males, different types of HPV can cause genital warts. Others types can cause cancers of the penis, anus, and back of the mouth and throat.

The Importance of Vaccination

Vaccines have been around long enough that many young people and parents are unaware of the devastation that infectious disease has caused around the world. Most diseases that used to kill or disable so many people are not present in the US any longer. Because of this, many people think that these vaccines are no longer needed. This is not so because most of these diseases can be found in other parts of the world.

One notorious, highly contagious disease left its mark on human history for 3,000 years before it was eradicated through vaccination. Smallpox infected 50 million people worldwide every year and killed nearly a third of those who contracted it. Survivors were left with disfiguring skin lesions (even on the face), total blindness, or both. In 1979, thanks to a global effort, 50 million cases of smallpox per year was eventually reduced to zero. Many other vaccine-preventable diseases have seen dramatic drops in infection rates. Polio is likely to be eradicated in the next few years.

To completely eradicate an infectious illness, high vaccination rates are necessary. For example, if a non-vaccinated person with measles enters a new community, they will have no impact on that community if all of its members are already immune to measles. This is called herd immunity. The concept of global vaccination and herd immunity may lull you into thinking your child is protected because of others, but this is not true. We live in a global community where people with serious infections can get around the world in a matter of hours. It does not take long for a contagious disease to spread among people who are unprotected. This has occurred recently with outbreaks of measles and mumps. Both diseases have serious health complications.

Keep in mind that vaccinating your child will protect others as well. People in certain populations or infants may not be able to get a vaccine. Having your child vaccinated protects your child and anyone they come in contact with.

Safety and Controversy

Vaccine safety has been a concern since they have been available, so the controversies are not new. Over the years, some vaccines have been recalled or linked to other heath conditions. Unvalidated information can lead others to think vaccines cause more harm than good, and this is not the case. Although there are some risks involved in getting vaccinated, they are overwhelmingly safe. The most recent public controversy concerns the MMR vaccine and its link to autism, a developmental disability. There was one, now retracted, study that showed this. However, there have been numerous studies since then that prove there is no link, but the negativity surrounding MMR safety persists.

As a parent, you need to have all the facts before you make a decision. Learn what ingredients are used to make a vaccine, the disease's history, and how it can affect your child and those around your child.

Most everyone, from infancy to adulthood, can be vaccinated. There are some considerations for certain populations, like transplant recipients or those with suppressed immune systems. These can be addressed on an individual basis.

Have an open, honest discussion with your child's doctor to address any concerns you may have about vaccination.

Revision Information

• Reviewer: Michael Woods, MD, FAAP
• Review Date: 02/2017
• Update Date: 03/01/2017