Is sepsis in teens rare?

Rare but possible. People can get sepsis at any age.
It can happen. Sepsis can happen in anyone depending on any underlying conditions, type of exposure, hygiene, vaccination status. The key is to be mindful during travel and up to date on vaccinations.
Yes. Sepsis at any age is rare. A major purpose of our immune system is to fight off bacterial invasion and prevent sepsis. This life treating bacterial invasion only happens when something is seriously wrong with our body and it needs to be promptly and appropriately treated with antibiotics in a hospital setting. If sepsis was common the human race would not be able to survive.