Is he still at risk of Chicken Pox even though he's been vacinated?

[Novella]

may just be a cold but no vaccine is 100% and I know of a few children who are vaccinated who got a mild dose of chicken pox

fx for you that its just a cold

[Tinks]

I have heard of kids getting a milder dose of Chicken pox if they've been immunised. You don't usually get a cough with the Chicken Pox virus, it's generally just a slight runny nose, headaches, aches and pains and fever.

[Phteven]

Yes. You can still catch chicken pox if you are vaccinated however it is likely to be a mild case.
Chicken Pox doesn't generally cause coughing.