Doc's confused logic
You should tell Dr. Hong [November 4, Dr. Hook: "Flu shots: Roll sleeves up... if you're elderly"] that "classical conditioning" is not an accurate way to describe the reason people believe the flu shot makes them sick.
The good doctor is confusing the phenomenon observed by Russian psychologist Ivan Pavlov with the logical fallacy that goes by the Latin moniker post hoc ergo propter hoc ("after that, therefore on account of that").
You may recall that the "classic" case upon which Pavlov based his definition of "classical conditioning" involved a dog, a bell, and a bowl of food. By repeatedly juxtaposing the three items, Pavlov noted that the bell eventually elicited from the dog the same response as the bowl of food. The dog's response is a valid neurological response.
Since your doc is saying that the flu shot-sickness association is an illusion, it would be more accurate to describe it as a post hoc fallacy.
Actually it's surprising that your editors let this slip. Probably the result of the classically conditioned post hoc fallacy that deference is the only proper response to a doctor.