If a vaccinated child gets 5 to 10 vesicular lesions 2 weeks after vaccination, can s/he attend school?

You cannot distinguish a mild case of varicella disease from a rash caused by the vaccine. The child may have been infected with varicella at about the same time s/he was vaccinated. The conservative approach would be to treat the child as if s/he had chickenpox and restrict her/his activities until all the lesions crust.