Clinical studies have shown that a maintenance regimen of BCG increases its effectiveness significantly, so it is well worth doing. However, there is no "set" protocol for this and there are several that are commonly used. The most usual is to have an induction period of six infusions, with the maintenance consisting of having BCG once a week for three weeks every three months for two years. Another, less common, is to have BCG once a month forever. And there are others.
You should discuss with your urologist the reasons for his choice of treatment timing if this concerns you. But in any case, maintenance of some type is the way to go!!
Best of luck
Sara Anne