I believe there are some studies out now (have to find them) that recommend no flu vac for foals before 8 mo or so (can't recall the exact time). The flu vac apparently interfers with the antibodies from the dam and is counterproductive to the foal.
Here, babies are born and the navel is sprayed with either 1% iodine or Novalsan several times a day for about 5 days. Within the first 12 hrs of life (sooner the better), the foal is given an E Coli Antigen liquid. If the dam has not received a 5 way a month prior to foaling, then the foals will begin shots around 4 months (no flu). If the mares have received the 5 way prior to foaling, then the foals begin shots around 6 months (no flu).
I am thinking there was a past post recently on LB that listed a link to the new recommendations- you might try a search for that info.