Lulu - children are encouraged (young children) because, like the elderly, they are considered to have a lower immune system and not able to fight it as well. They also have reduced strength (I'm not talking brute stregnth either) to fight the condition which can be pretty foul. The flu can cause secondary conditions including pneumonia and other respiratory conditions. So anyone who has a respiratory condition (such as Asthma) or has recently had pneumonia is usually encouraged to have the vaccine - it is much more dangerous for them to get the flu. Also anyone with a lowered immune system (cancer patients, HIV patients, the very young, the elderly, pregnant women etc).

Did that make sense? My coffee fuelled brain power is just about depleted. Must recharge.

ETA: Oh, and the swine flu showed last year that it is much more volatile and problematic in young healthy people (as well as those with comorbidities). They urge ALL young, fit, healthy people to get the swine flu vacc.