I had my second booster the weekend before last (and had the usual tiredness, headache, muscle aches and shivers the following day). There was a huge difference with when me and Joe went for our first boosters last October and back then had to queue with around 100 in front of us.
On this occasion there were no queues, two tables set up in the vaccination hub and the nurses were standing there waiting for people to come through the door so there appears to be very little take up of the fourth vaccination.