Immunity to some immunizations wears off after a while. At that time, a "booster" dosage is required to restore immunity levels. This booster dosage is normally administered many years after the original series of vaccination shots. People who have previously received all their recommended childhood vaccines may still be at risk for developing life-threatening diseases after their immune systems have already been stimulated by previous exposures. For these individuals, new vaccinations will provide continued protection. The timing and type of vaccine used as a booster depends on when you last received an adequate dose of the initial vaccine series. If you were not given a booster dose within 10 years of your first exposure, another vaccine should be given. The second vaccine should be given at least four weeks after the first. Some vaccines require more than one injection to deliver a complete dose. A booster shot is needed if your body has not produced enough antibodies against the virus or bacteria. For example, people who have previously received a vaccine against tetanus, diphtheria, and pertussis (whooping cough) need a booster shot with tetanus and diphtheria toxoids and pertussis adsorbed (DTaP) vaccine to maintain protection.