Booster injections are also known as "reinforcement vaccinations," "booster shots," or "additional doses." These are vaccines that are administered to individuals who have already received an initial vaccination, but whose immunity may have waned over time. Booster injections serve to stimulate a stronger and more sustained immune response against the specific disease that the initial vaccine targeted. Other synonyms for booster injections include "supplementary vaccinations," "follow-up shots," and "repeat immunizations." While booster injections are typically given for childhood vaccinations, such as those for diphtheria, tetanus, and pertussis, they are also recommended for adults for certain diseases, such as hepatitis B and influenza.