The simplest way to determine your immunization status is to check your medical records. Contact your previous doctors for information about your past immunizations. Immunization information systems (IIS) — computerized systems that keep confidential immunization records of people in a specific region — also may be helpful. Contact the local or state health department for details.
If you have unknown or uncertain immunization status, you're considered susceptible to an infection and your doctor may recommend vaccination — either immediately or on an age-appropriate schedule. Generally, vaccinating someone who's already immune isn't considered harmful.
Another option is a blood test to check for the presence of antibodies to certain infections, such as measles, rubella, hepatitis or tetanus. Antibodies are substances produced by the immune system in response to natural infections or vaccination. If you have antibodies for certain infections, you're considered immune.
Keep in mind, however, that vaccines offer protection from a variety of serious or potentially fatal diseases. The surest way to immunity is to receive a vaccine.