Inactivated vaccines are made of killed bacteria or viruses that have been inactivated by chemicals or heat.
These vaccines are safe and stable, and they cannot cause disease. However, they stimulate a relatively weak response from the immune system, so people usually need several booster shots.
The flu shot is an inactivated vaccine. Live attenuated vaccines are made from live but weakened microbes. The vaccines for measles German measles and mumps are made from live attenuated organisms
The microbes are weakened by growing them under special conditions in tissue cultures in the laboratory. Because these vaccines stimulate the immune system more strongly, people usually need only one booster. Most of these vaccines are injected, but some, such as the Sabin polio vaccine, can be given by mouth.
Very rarely, the weakened microbes in a live vaccine can change to a virulent form that can cause disease, for example the H1N1 vaccine in 1976 . As a precaution, doctors do not give live vaccines to pregnant women or people with damaged immune systems, such as those with human immunodeficiency virus (HIV) or cancer or those who take medicines that suppress their immune systems.
Your doctor can tell you if you should avoid having a certain vaccination. Many microbes that infect people are not harmful themselves, but they produce toxins—very powerful poisons that cause illness. Vaccines that protect against toxins must be made from inactivated toxins, called toxoids. Chemicals are used to inactivate the toxins so that they are harmless but still capable of stimulating antibodies.
Toxoids are used to immunize people againstdiphtheria and tetanus. After you receive a vaccination against tetanus, you develop antibodies to the toxoids or antitoxins. We have vaccines to protect us against diseases such as smallpox, polio, measles, mumps, chickenpox, and flu. But as yet, there is no vaccine against acquired immunodeficiency syndrome, better known as AIDS.
What about cancer?
Some experimental vaccines against cancer are being tested. Immunologists are searching for certain antigens on the surfaces of cancer cells in their efforts to produce cancer vaccines.