I would guess Guillain-Barre, since that is triggered by some viral infections and also sometimes vaccination (perhaps the same underlying reason). It affects very few people after vaccination, but that information is not going to be much comfort to the people it does impact. It is one condition that is a known risk factor for certain vaccines (or of various viral infections). That it could have happened anyways, from an infection, is also probably not much comfort to those who end up with it.