Assuming that four of the six Mandelstam invariants which describe vector meson production are independent of the vector meson mass λ, we show that vector meson dominance must be written in the helicity frame. We point out that this assumption cannot be justified with kinematical arguments only, and show that it is correct at high energy in various models, including evasive and conspiring Regge-pole exchange, as well as Regge-pole model with absorption. However there remain difficulties with trajectories of the A1 and B type.