First of all, influenza is not "an unharmful disease". It's can be a serious threat to people with a lowered immune system like people recovering or suffering from other diseases. That's why people die from it and end up in the statistics.
If it could have been exterminated like some other diseases in the past we would have, scientists have trying and working long enough on it.
If it could have been exterminated like some other diseases in the past we would have, scientists have trying and working long enough on it.