7 year old woke up w/ sore throat and vomited once. now running low grade fever (99.5). strep neg. how long should i expect low grade fever to last?

Viral fevers: Fevers due to viral infections typically last 3-5 days, but can occur for 7-10 (less common). The trend of the fever is more important than the duration of fever in many cases. For instance, illnesses that start with high fevers which decrease with time are less concerning than those that start low but increase in degree over the course of days.