Vaccines can be divided into two major categories. Most vaccines are derived from parts of dead germs or the whole dead germs, but some vaccines actually contain live germs. They are made differently because some germs cannot trigger the alarm in your immune system once they are killed, so they must be presented to your immune system alive.

Before you start to get queasy from the thought of having live germs injected into your body, keep in mind that there are already live germs living inside your body. In addition, when you eat a plate of salad, you are in fact ingesting live plants. And if you are not a strict vegetarian, you are consuming animal carcasses every time you bite into a steak or a chicken drumstick. It sounds gross when you think about it, but the reality is that having other life forms in your body is neither unusual nor unnatural.

Vaccines Derived from Parts of Germs

Many vaccines are made from parts of germs. These vaccines cannot cause an infection because a single body part of a germ is not enough to allow the germ to spread in the body or cause any illness. Think of these vaccines as the physical characteristics of a terrorist for the police file, such as a tattoo or dental record. The police can safely keep this information in their headquarters without fearing the information causing a threat to security. The list of vaccines that are made from germ parts include vaccines against hepatitis A, hepatitis B, Haemophilus influenza type B, pneumococcus, and certain flu vaccines.

Vaccines Derived from Toxins

A few vaccines are designed from poisons created by germs. These vaccines work by alerting the body's defense to the toxin released by germs, giving the immune system a head start in getting rid of these poisonous chemicals. You can think of these types of vaccines as blueprints to the germ's weapons. Once again, these “blueprints” can be safely stored in police headquarters without compromising the security of the complex. A weapon is quite harmless unless it falls into the wrong hands. Inside the body, these modified toxins cannot be activated by anything, so they can only trigger the immune system and do not cause any problem. Examples of this type of vaccine include the tetanus and diphtheria vaccines.

Vaccines Derived from Dead Germs

Some vaccines are produced from killed germs. These vaccines work by providing the immune system with a complete physical description of these germs, so when these germs attempt to invade the body, the body's defense will recognize them immediately and thwart their invasion. These vaccines cannot cause a real infection in the person receiving the vaccine because dead germs are unable to carry out their bad deeds. Vaccines that use this mechanism include polio, rabies, anthrax, typhoid, Japanese encephalitis, cholera, and most flu vaccines.

Vaccines Derived from Live Germs

Some people consider these types of vaccines the most dangerous because they are made from live germs. However, the germs in these vaccines are severely weakened. Nevertheless, they can cause a mild infection in the person receiving the vaccine. You can compare these types of vaccines to the police holding terrorists in custody. They do pose a security risk to the defense system, but they can yield even more valuable intelligence than a killed enemy because they can be interrogated by the body's immune system. If these bad guys escape from custody, your body may experience a very weak but real attack by these germs. The good news is that the mild case of the infection is never dangerous to a healthy person. Nevertheless, people with severely weakened immune systems should generally avoid getting live vaccines. Vaccines that fall under this description include measles, mumps, rubella (German measles), chickenpox, yellow fever, tuberculosis, and certain flu vaccines (the nasal spray flu vaccine, tradename FluMist).