Thanks!!I do not know that - the only thing I know is when I was helping a friend with direct imports of saltwater fish - we never, ever use prophylactic treatment. The few times when we get a disease (mostly white spot) they was treated separately with copper. we are talking about around 20 - 30,000 fish during a 18 years period. My friend was known to have among the best fishes in our area (southern Sweden)
The largest importer in Sweden of fresh water ornamental fish does not either use prophylactic treatment at that time (now - I do not know)
For me vaccine is not an prophylactic treatment - and in the other case you mentioned - there was (is) indications of a disease or pathogen. Its the same for me - I know that in all my stomach surgeries - I have got Metronidazole as prophylactic agent against infection of the stomach lining - and I thankful that all my use of this compound in my aquariums back in the 70 - 80 ties not had lead to a resistant gut flora. But the interesting thing is that it needs to be an indication of a disease (or pathogen)
There is another good example of vaccine - that for the measles. It was nearly eradicated here in Sweden 20 years ago but because of lower vaccination rate among immigrants and because of the anti-vaccine movement we have rare outbreaks now and than
Sincerely Lasse