I am in the same situation with chronic immune deficiency due to medication. You have to go some places other places you can avoid. Unfortunately hospital/GP appointments are the most important yet most dangerous. I put a little Vaseline inside my nose and don't touch anything in the Surgery without putting anti-bacterial gel on my hands before and after. Avoid sitting next to anyone and try not to go to the bathroom. It may be wise to phone your GP surgery explain the situation and they may find a separate room for your FIL to sit in while waiting for his injection.