Over the last year I've accuired about 10-15 vandas and it's quite common for them to do this when they get moved. Vanda really like stability, and they can take a few months to get over their 'sulking'. Also stay quite mild on the fertilizer until they pick up again.

Good luck!

Take a look at the lower leaves, there seems to be some irregularity in the pigmentation. Vandas drop leaves for several reasons; stress, shock, age, pests, or bacteria.
I say regular fertilizing because this combined with superthrive will promote lots of new roots which is where it all starts. Systemic fungicide is recommended and maintain care and observation.