Preschool boosters

In the uk when child is 3years and 4months they are offered a preschool booster.

It’s a booster of the ones they give when baby and a year old

Is it really necessary?

He been at nursery for years (pretty much ill at least twice a month)

Every time he has vaccines previously he would get really ill and it would last for days.

He just getting over an ear infection so is it sensible to get booster now or ever?