The answer appears to be ... it depends.
Early Oseltamivir Treatment in Influenza in Children1-3 Years of Age: A Randomized Controlled Trial
A study in 2010 out of Finland by Heinonen, et al showed that if given in the first 12 hours of symptom onset to otherwise healthy pediatric patients between the age of 1-3 years:
- decrease incidence of acute otitis media by 85%
- no difference if given within 24 hours
Among children with influenza A, oseltamivir started within 24 hours of symptom onset
- shortened medium time to resolution of illness by 3.5 days (3.0 versus 6.5) in all children
- shortened median time to resolution of illness by 4.0 days in UNvaccinated children
- Reduced parental work absenteeism by 3 days
* no differences were seen in children with influenza B *
- Single Center study in Finland
- The authors received support from the drug manufacturer
- The sample size of children with confirmed influenza cases with small (influenza A: 79, influenza B: 19)
If you have a patient between the age of 1-3 years with very early symptoms concerning for flu, a positive rapid influenza A test could allow you to cut her symptoms by 3 days, prevent complications, and allow parents to go back to work sooner.
Heinonen S, Silvennoinen H, Lehtinen et al. Early oseltamivir treatment of influenza in children 1-3 years of age: A randomized controlled trial. Clin Infect Dis. 2010;51(8):87-94.