I read about a vaccine given to cats to make them less allergenic.  Is that true?

Not only is it true, but it works.  Swiss scientists coupled cat feline protein number one (the cause of most human cat allergy) to a cucumber mosaic virus and vaccinated cats.  The vaccine was safe for the cats and led to a marked reduction in their feline protein number one.

This research could provide a revolutionary new approach to humans with cat allergy:  making their cats “hypoallergenic”. The Swiss scientists also posited that the cats will also benefit because of improved relationship/fellowship with their owner.