Talk to the doctor. However, I know that some tests look for the antibodies for a disease rather than an active virus/bacteria. If they look for the antibodies then it would be positive, because the point of a vaccine is the body will create antibodies. However, knowing that he had the vaccine, I don't know why they would test for it if it was an antibody test. Here is a the Wiki page, don't know if it has anything useful though http://en.wikipedia.org/wiki/Haemophilus_influenzae
Call the doctor, he/she should be able to explain it to you and let you know if it is something to worry about or not.
State Certified Early Childhood Special Education Teacher
New Mom as of March 2009!