Greyhound with itchy irritable skin

[MsAdorabelleDearheartVonLipwig]

My aunt and uncle have a rescue greyhound. They've had him about four years. Last year his booster injection was changed to a different sort and my aunt and uncle swear that this was when he started to have problems with his skin. He is very sensitive and scratches all the time. The vet thus far hasn't been an awful lot of help apparently so I thought I'd ask if anyone here has any advice.

If they think it's the brand of vaccine, get them to phone round any local greyhound rescues and ask if they have changed vaccines and experienced any similar side effects.
They will be vaccinating countless greyhounds so if there is any issue, it will show up there quicker , rather than asking the vet if they've had any reports back.
I;d imagine only a small % of the dogs they see at a regular vets are greys.

And has he changed food or has the food itself been new and improved?
IIRC they are sensitive to some things (I think wheat is one) .

Thanks. I don't think he's changed food but that's a good idea about phoning round rescues.

not really a lot of help but I just wondered
has his bed been washed in a harsher detergent/softener
has he been washed with a differant shampoo
has he been out in dry weather when there would be pollen/grass dust
if he is a true grey he would have very little fur to protect his skin
My lurcher had previously had problems with irritation on his legs caused by irritants from numerous sources (he has very little fur on his legs)
sorry if I am way off beam and you have already considered all the above