what a way to begin! In addition to the other good advice about educating him about not sharing combs, hats, etc., I'd add that a lot of lice are resistent to the over the counter meds. What is effective 100% of the time, if you are vigilant, is checking for nits, and then coming then out. The Licemeister comb, which you can google and buy on-line, is the best, because it is very fine toothed. When my daughter got lice last year and the over the counter meds didn't work (we treated everyone in the family, laundered everthing, bagged things that coudn't be washed - we were vigilant)- we researched, researched, and ended up going the combing only route. Every morning, every evening - we'd sit my daughter in fron of a video on our laptop at the kitchen counter, where the light is brightest, put detangler on her long, long hair and meticuloulsy comb until we didn't see anymore nits. Took only a few days until there were no nits, but we checked for two weeks, to make sure. Takes time, but it's non-toxic and effective. And by the way, lots of schools will let kids in school with nits, as long as you're treating, and lots of school nurses understand that lice are more an more resistent to meds and accept combing as an appropriate treatment.
Good luck! Hope you don't actually have to do any of this, but if you do - it's only time, no one is sick or in pain, and it will pass.
A.