How do vaccines work? Think of it as your body’s defense system getting secret information about the enemy before the battle even begins.

There are two basic groups of vaccines and both give the immune system a sneak peek at the defense mechanisms and weaponry employed by a germ. This advance notice allows the immune system to build safeguards called antibodies. Antibodies, proteins produced by the immune system, are able to rapidly recognize and neutralize the germ minimizing the damage done.

The first group of vaccines is made from pieces of the germ. Some in this group consist of whole germs that are inactivated or killed by using chemicals or heat. Others consist of a single bit or piece of the germ, usually a part from its outer coating. Diphtheria and tetanus vaccines are made from toxoids. Toxoids are a toxin rendered harmless by heating or chemicals. In the case of tetanus, the germ makes tetanus toxin that targets nerves causing painful muscle spasms commonly referred to as “lockjaw.” The tetanus toxoid in the vaccine induces the immune system to make antibodies that neutralize the tetanus toxin thereby providing protection.

The second vaccine group is comprised of live vaccines such as MMR (measles, mumps, and rubella), and nasal flu vaccines. Live vaccines are weakened germs that the body is able to easily kill and then make antibodies to protect for future exposure. The process is akin to making Pit Bulls into Chihuahuas. Both breeds are recognizable as dogs but the Chihuahua has little or no bite. The immune system recognizes the vaccine and develops a very strong immune response, just as it does the actual germ, and develops defenses to protect against exposure without the person suffering from the actual illness.

The major drawback of live vaccines is that immunocompromised people, such as people on chemotherapy or other medications that weaken the immune system should not receive them. Their immune systems may have difficulty fighting even a weakened germ. In cases of severe impairment, the recipient could develop a serious, life threatening illness from the vaccine. In general, household members of an immunocompromised person may receive live vaccines.

Immunocompromised people should also stay away from people with a chickenpox rash following varicella vaccination as the vaccine virus may be transferred from the rash and should not handle the diapers of babies that have received the rotavirus vaccine in the past 30 days.

Both groups of vaccines operate by giving our immune systems a head start when dealing with germs. Vaccines give you the benefit of protection but without the risk of serious illness that can occur with the actual disease. They are safe and effective when used properly. You should always ask your healthcare provider if you are concerned about whether a vaccine is safe for you or your household members.

Vaccine Smarts is written by Sealy Institute for Vaccine Sciences faculty members Drs. Megan Berman, an associate professor of internal medicine, and Richard Rupp, a professor of pediatrics at the University of Texas Medical Branch. For questions about vaccines, email vaccine.smarts@utmb.edu.

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