How many years of oral antibiotics prophylaxis do you recommend for a teenager with hereditary spherocytosis post-splenectomy?

If older than 5 and vaccinated, no proph.

No prophylaxis is required for teenager post-splenectomy, either in hereditary spherocytosis or ITP. A better strategy is to have Amoxicillin available at home only to be given at the onset of fever before seeking medical attention. Below the age of 5 years, daily prophylaxis probably makes sense.