Perseid activity may wane by about 25% when Comet Swift–Tuttle is farthest from the Sun.
The comet’s distance from the Sun affects how much fresh dust and gas it releases during its orbit. Near the Sun, stronger heating can drive more activity and replenish the surrounding debris environment. Farther away, the comet is much less active.
The annual shower does not disappear when the comet is distant. Dust from many earlier passages has spread around much of the comet’s orbit, so Earth can continue encountering Perseid particles even when Swift–Tuttle is near aphelion.
This percentage is an approximate modeled change, not a prediction that every observer will count exactly one-quarter fewer meteors. Moonlight, weather, light pollution, radiant altitude, and natural variation can have a larger effect on a particular observing session.