Viral infection is listed as a side effect for some medications. How does that work? Shurely it doesn’t mean that the medication is contaminated with a virus?
Do they mean that it weakens your immune response?
How would your immune response be weakened, but only to viruses? What about bacteria + fungi?
My WAG: the medication lowers your immune response such that a virus that was already lingering around flares up. Could just as likely have lead to a bacterial or fungal infection. The virus happened to get there first.
Alternate WAG: The medication is an antibiotic, say a topical antibiotic, used prophylactically. In this case, the medication would suppress bacterial overgrowth, but won’t touch a viral infection if it decided to start.
If WAG #1, why not list the side effect as a weakened immune system? I would think the lawyers would want to be able to say “we told you it could happen” to the person who used the product + got a bacterial or fungal infection.
WAG #2 makes more sense, but I seem to recall things like alergy meds having this disclaimer. I’ll poke around for specific examples.
WAG 1 rebuttal: Saying “weakened immune system” alone might be too vague, legally. Someone could argue that the Mycobacteria infection they got after handling sick fish wouldn’t have taken hold if their immune systems hadn’t been compromised by Medication X.
WAG on top of WAG. Off to a great start this week!
IANAL, but I would think that would cover their asses better legally. I get the idea that the side effects are listed as much to cover Giant Evil Corporation’s ™ ass as to warn consumers. All they have to do is say “We told you it was a possible side effect,” and they’re off the hook.
Advair lists viral infections of the eyes, skin, + resperatory tract.
Prehaps this is related to WAG #2: It’s an inhaler for repeated use, so it probably has antibacterials/antifungals in it to prevent bacteria+fungi from growing. Antivirals require active viral replication IIRC, so they would be ineffective.
I think I’m going to go with WAG #2 for now, unless someone comes up with and educated guess or even a factual answer! 
Fine then 
Herpes virus often will recrudesce in response to drugs that affect the immune system.
Pigs seem relatively resistant to this phenomenon:
http://www.springerlink.com/content/ur1g08728n428ll6/
Keep in mind that while injectables, ophthalmics, and (I believe) inhaler products are sterile prior to opening the package, other medicines (orals, suppositories) are not. They aren’t full of contaminants, either, they just aren’t sterilized during manufacturing (although raw drug product does have to have certain minimums of bacterial growth in them).
I think that medicine with side effect warnings such as those in the OP are meds that significantly increase the patient’s susceptibility to infection.
Ultimately, it means that the group taking the drug had a higher rate of viral infection than those in the group of those taking a placebo. It could be caused by the drug, or by other factors that affected the one group and not the other during testing.
They have to report what they found in their studies. If they say viral infection, that’s because viral infection was one of the most common things that happened to their test subjects. If they don’t say bacterial infection, that’s because that wasn’t one of the most common things. They could theorize that the viral infections came about because of a weakened immune system, but they’d have to prove that that’s what was going on before they could put it in their ads (if the FDA even allows that - I don’t know that they would), and frankly it’s not important enough to warrant further research.
There are drugs that impair the immune system, and that information can be found on some package inserts, like for Enbrel. Some steroids, which prescription nasal spray contains, can impair the immune system. Also, as others have said, anything that occurs during a study must be reported as a possible side effect.
Advair contains a steroid, when applied topically to the inside of the airway it could suppress local immune response. Upper airway infections are almost always viral in origin,
IANA phamaceutical researcher
For some things, it could just be that someone in the test group got a viral infection while testing the medication, so they had to list it.
Thanks for all of your replies.
I used to work as a QC Microbiologist for a drug company. Great money, but I felt the ethics to be a little iffy, to say the least, so I quit. I know drugs are often loaded with microbes.
I think Smeghead hit the nail on the head. The increased viral infection in the study may or may not be because of an overall decrease in immune response, but it’s not important enough to warrant further study.