Immunity: Protection from an infectious disease. If you are immune to a disease, you can be exposed to it without becoming infected.
Vaccine: A preparation that is used to stimulate the body’s immune response against diseases. Vaccines are usually administered through needle injections, but some can be administered by mouth or sprayed into the nose.
Vaccination: The act of introducing a vaccine into the body to produce protection from a specific disease.
Immunization: A process by which a person becomes protected against a disease through vaccination. This term is often used interchangeably with vaccination or inoculation.
We become immune to (or protected from) a disease when our bodies create specific antibodies to fight that disease. Vaccines contain ingredients that help your body build this immunity.
Vaccines need to be safe and effective. Certain ingredients help keep vaccines safe from contamination and toxins. Others, like stabilizers, help vaccines stay effective for a long time.
All vaccine ingredients help to make a vaccine as effective as possible, while being safe. Ingredients like aluminum salt help boost the body’s response to the vaccine.
Purpose: To keep the vaccine effective after manufacturing
Most commonly found in: Jell-O®, naturally in the body
Examples: Sugars, gelatin
Purpose: To help boost the body’s response to the vaccine
Most commonly found in: Drinking water, infant formula, and some health products such as antacids, buffered aspirin, and antiperspirants
Examples: Aluminum salts
Purpose: To kill viruses or inactivate toxins during the manufacturing process
Most commonly found in: Naturally in the human body, fruit, household furnishings (carpets, upholstering)
Examples: Formaldehyde†
Purpose: To grow enough of the virus or bacteria to make the vaccine
Most commonly found in: Eggs, and foods that contain eggs
Examples: Egg protein^
Purpose: To prevent contamination by bacteria during the vaccine manufacturing process
Most commonly found in: Common antibiotics. Antibiotics that people are most likely to be allergic to—like penicillin—aren’t used in vaccines.
Examples: Neomycin, Kanamycin, Streptomycin
Purpose: To prevent contamination
Most commonly found in: Some kinds of fish
Examples: himerosal (only in multi-dose vials of flu vaccine)*
Most vaccines do not have any mercury in them. However, multi-dose flu vaccines and one type of Td vaccine contain a small amount of thimerosal. Thimerosal contains a form of mercury (ethylmercury) that does not cause mercury poisoning and is safe for use in vaccines. Flu and Td vaccines are also available in thimerosal-free versions.
Vaccines can help protect against certain diseases by imitating an infection. This helps teach the immune system how to build immunity to fight off a future infection. Different vaccines provide immunity in different ways.
Immunity to a disease is achieved through the presence of antibodies to that disease in a person’s system. Antibodies are proteins produced by the body to neutralize or destroy toxins or disease-carrying organisms. Antibodies are disease-specific. For example, measles antibody will protect a person who is exposed to measles disease but will have no effect if he or she is exposed to mumps.
There are two types of immunity: Active and Passive.
Active Immunity results when exposure to a disease organism triggers the immune system to produce antibodies to that disease. Active immunity can be acquired through natural immunity or vaccine-induced immunity.
Either way, if an immune person comes into contact with that disease in the future, their immune system will recognize it and immediately produce the antibodies needed to fight it. Active immunity is long-lasting, and sometimes life-long.
Passive immunity is provided when a person is given antibodies to a disease rather than producing them through his or her own immune system.
The major advantage to passive immunity is that protection is immediate, whereas active immunity takes time (usually several weeks) to develop. However, passive immunity lasts only for a few weeks or months. Only active immunity is long-lasting.
† Formaldehyde is diluted during the vaccine manufacturing process, but residual quantities of formaldehyde may be found in some current vaccines. The amount of formaldehyde present in some vaccines is so small compared to the concentration that occurs naturally in the body that it does not pose a safety concern.
^ Because influenza and yellow fever vaccines are both made in eggs, egg proteins are present in the final products. For people with egg allergies, there are now two new flu vaccines available. People with severe egg allergies should be vaccinated in a medical setting and be supervised by a health care professional who can recognize and manage severe allergic conditions.
* Thimerosal contains a different form of mercury (ethylmercury) than the kind that causes mercury poisoning (methylmercury). Ethylmercury is safe to use in vaccines because it’s processed differently in the body and is less likely to build up in the body—and because it’s used in tiny amounts. Even so, most vaccines do not have any thimerosal in them. Learn more about thimerosal, mercury, and vaccine safety.