On the community thing, there hasn't been an outbreak of this sort of 'flu for a very long time consequently there was relatively little immunity in the general population. One group that did have some immunity was the elderly who had been exposed previously. This is probably one of the reasons that there were relatively few deaths in that section of the population. Getting your son immunised now would mean that if at some point in the future this sort of virus re-occurs then he would have at least some immunity. There is still a long term potential benefit to getting this jab.
There are of course just possibilites (like the side effects) and are by no means certain. You should probably treat this advice like all medical advice received on a bike forum, with suspicion.