This study presented a mathematical model of
Influenza A (H1N1) with age three groups. Parameter
estimation is carried out using the least square method to
the 2009 pandemic influenza incidence data in Korea.
The relative errors of incidence peak were 0.00003,
0.0004, and 0.0013 for each group, and the fit of model
with the 95% of confidence which was calculated by the
Bootstrap method was given. The basic reproduction
number R0 was 1.44 and it reduced to 1.14 after
implementation of intensive interventions.