Explaining How a Vaccine Works
Vaccines hold up a “Wanted” photo of the bad guy — the pathogen or germ. Each vaccine is a little different, but they all show our immune system something super recognizable about the pathogen. That way, if we are ever exposed to this pathogen, our immune systems will respond to it.
The “Wanted” photo can be some bit from the outside of the pathogen, like a specific protein or sugar. These bits act as a way to identify the pathogen, similar to the way a tattoo or birthmark helps you identify a person. The vaccine version may attach this “Wanted” photo to a warning, like a blinking red light, such as a protein that will create a stronger immune response.
Other vaccines may be the equivalent of a head-to-foot photo; some vaccines use the whole pathogen (in a killed vaccine, explained more in Chapter 5) or in a live, but safe, similar version. Chapter 7 discusses the ingredients that typically make up vaccines.
Find out more about the basics of how a vaccine works in the following sections.
Distinguishing between antigens and antibodies
Antigens are what is memorable in the “Wanted” photo. An antigen is something very specific — like that birthmark or tattoo — that can’t be missed. Your immune system uses that very specific marking to create an immune response and memory. This marking is usually a protein or sometimes a sugar on the outside of the pathogen.
Antibodies are what your body makes in response to antigens. After your body has been shown the antigen or “Wanted” photo, you keep a supply of memory immune cells that can make a whole lot more antibodies if the pathogen ever arrives. Specific antibodies go after just one specific antigen. Once that antigen is found again, your body floods it with copies of this antibody from those memory immune cells. The antibodies then attach themselves to their antigens, which are on the outside of the pathogen. The antibodies then stop this specific pathogen, like a virus particle or bacterium cell, from causing any more problems.
It typically takes a few weeks after exposure for the body to produce this response. Vaccination gives you a head start so you already have the ability to make all these antibodies if you need to. With a natural infection, you can get quite sick before you were able to scramble and create an effective immune response.
Breaking down other vaccine ingredients
Vaccines contain more than just the “Wanted” photos, called antigens, that help your immune system identify pathogens (see the preceding section). Other ingredients are needed to make sure the vaccine works as it should:
Some of these “Wanted” photos don’t create much of an immune response. The immune system needs to be alerted to the fact that this “Wanted” photo is important to remember. Vaccines may include an alert, which acts like a red blinking light, saying “pay attention here.” This ingredient may even be directly attached to the “Wanted” photo. Such alerts when added to the vaccine mix are called adjuvants. A common adjuvant includes aluminum, also found in drinking water, antacids, and antiperspirants. We discuss the ingredients that go into vaccines more in Chapter 7.
Vaccines also may contain stabilizers, much like some of our food does. These include sugars and gelatin (also found in Jell-O) that keep the vaccine ingredients well mixed, so they don’t separate or deteriorate.
Vaccines can sometimes include preservatives to keep mold or bacteria from growing in the vaccine, much like we would have in a bottle of jam at home. Just as many foods are advertised as preservative-free, many vaccines are too. Preservatives are particularly used in multi-use vaccine bottles, especially for the flu, as these are kept open longer to vaccinate multiple people. In some cases, this can include thimerosal, which contains mercury, but it’s a type of mercury that doesn’t have the same worrisome risk as the mercury found in fish. Children’s vaccines do not include mercury, except in rare cases with multi-use flu vaccine vials and some specific brands of tetanus shots for adolescents.
Vaccines may also include trace amounts of chemicals used in their production. These substances are removed, but sometimes a very small amount remains. In order to include a whole virus or bacteria but make sure it’s dead and won’t make copies of itself, formaldehyde is used. The amount used in a vaccine is much, much less than we naturally have in our bodies.
Sometimes antibiotics, usually not the sorts we are allergic to, are used to keep bacteria from growing during production. These antibiotics are removed at the end, so at most only a tiny amount remains. Eggs are used to grow some viruses used to make vaccines, and so egg proteins, in very tiny amounts, may be present in some specific vaccines.
Comparing Viruses, Bacteria, and Toxins
Viruses are super tiny particles, made of genetic material surrounded by a protein shell. They can make copies of themselves only inside of other cells.
Bacteria are more complicated; they are single-celled, living organisms that can usually make copies of themselves on their own.
Viruses, the smallest of the common pathogens, are protein shells with a bit of genetic instructions tucked away inside. Viruses use these instructions inside another cell, such as our own, to make copies of themselves; in the process our cells may be damaged by the virus or our immune system’s response. Because viruses can’t make copies of themselves on their own and need to be inside a cell, they aren’t considered fully alive. We go more in-depth about viruses in Chapter 2.
Pathogens also include bacteria, as we talk about in Chapter 4. These are made up of a single cell that can reproduce on its own. Some bacteria invade your cells; others remain outside; some may do either. You have lots of bacteria inside your body at any time. In fact, we have more bacterial cells than human cells in our bodies. Our skin and gut and immune systems keep these bacteria