(a) Pandemic influenza is not business-as-usual influenza. Bear this in mind. (b) You wouldn't call a tiger a cat.
(a) business as usual = no changes, nothing special, nothing unusual, same as before, common
(Pandemic influenza, as you know, is a form of influenza that jumps from continent to continent. The writer is saying that it's not the usual, every day variety of influenza, but something much worse, much more dangerous, much more deadly.)
1) When John got out of prison, it was business as usual. Within a week he had robbed two stores.
2) The wife invited her husband to return home. Within hours, it was business as usual. He had beaten her again.
3) He returned home after three years in the army. Within days, it was business as usual. He was working on the farm, dating the girl next door, and seeing his friends after work.
(b) In the last sentence, the writer is reinforcing what was said in the first sentence. Pandemic influenza is not to be confused with less lethal, less dangerous forms of influenza. You wouldn't call a tiger a cat, and you wouldn't call pandemic influenza "just another influenza". By the way, this is not an idiomatic expression commonly used by native speakers, but a creation of the writer.
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