Pediatric fever without source – when to do a septic workup?

Agree on urine. Use the Rochester or Philadelphia criteria if you're on the fence. If the child is well-appearing and you can ensure solid follow-up, a watchful waiting approach with clear return precautions is reasonable.

At 9 months and fully vaccinated, the risk of occult bacteremia is very low. For a well-appearing child I'd do a UA/urine culture (UTI is still the main concern in this age group) and reassess. I wouldn't reflexively LP a well-looking vaccinated infant.