There are a lot of scare stories about the effectiveness of the vaccines, in particular the AZ (who do not have the PR back up that Pfizer has).
You might want to have a read of this article though (which seems to have been kept rather hidden). I’ve read similar elsewhere too, and I think we are just about to get some relevant research positive info from South Africa about AZ.
The focus always seems to be just on antibodies, which form only a small part of our immune response to the vaccines. Antibodies naturally wane over time, so they will drop off. However the vaccines will also have encouraged T cell protection, and T cells last a very long time. The T cells are the heavy artillery of the immune system, they can attack the virus when it has entered cells. Antibodies can only stop the virus before it latches on to the cells.
Also I notice that you had your first two vaccinations 5 months apart. That is actually very good. The reason boosters are required are because the first two jabs for most people were too close together (often 3-4 weeks in the US, though spaced more like 10 weeks for us in the UK). The close spacing did not allow broad immunity to build up. (Everything was speeded up in the rush for vaccines.) Boosters were supposed to be after 6 months to get that broad immunity but governments panicked when omicron turned up and reduced the gap down to 3 months.
TWIV (This week in Virology) on Youtube has covered this a great deal (about the confusion about antibodies and actual immunity, and the short versus longer time between first and second vaccinations). Check out the session where Paul Offit spoke (he advises the US government) as he spoke very clearly on this (his interest is virology in children so knows how to talk in clear, understandable ways!).
Antibody levels are very easy to check - T cell levels are much harder to check and why there has been less published research on them, in relation to Covid.
You are probably better protected than you think. Do also read the news updates for MS people from Dr Giovanonni. You should find links to them under the Everyday living section on this forum.
The other thing to consider is the best masks for you in terms of protection of yourself. There were two very recent articles in the Guardian that are worth looking at, if you haven’t already seen them. In your case I’d want at the minimum FFP2, and would ideally want FFP3 for more at risk areas (and make sure that they have the proper certification - there are some with false certification). In terms of comfort and fit the Korean ‘fish’ shape ones seem very reliable. I’ve just ordered FFP2s and FFP3s in that style (they are now being made in that style in the EU btw - you don’t have to get Korean made ones).