Only when a disease has been eradicated worldwide, as in the case of smallpox, is it safe to cease vaccinations for that particular disease. My child does not need to be immunized if he's healthy, active, and eating well. Vaccinations are intended to help keep healthy children healthy. Because vaccines work by protecting the body before disease strikes, if you wait until your child gets sick it will be too late for the vaccine to work. The best time to immunize your child is when he is healthy.
Immunity only lasts for a little while.
A few vaccines, like the one for measles or the series for hepatitis B, may make you immune for your entire life. And some, like pertussis, wear off but do not require boosters because the disease is not considered dangerous among adolescents and adults. It is important to keep a record of your child's shots so you will know when he is due for a booster. The fact that vaccines are continuously studied and improved implies that they are unsafe. The Food and Drug Administration's Center for Biologics Evaluation and Research is the government agency responsible for regulating vaccines in the United States.