system
Given the following post, respond as if you're commenting on Reddit:
human
If the symptoms of flu(fever, coughing) are from the immune response, rather than the virus. Why don't we get flu like symptoms after a flu vaccine?
gpt
Those that are applied by injection are inactivated flu viruses, so they don't have the ability to actually infect cells. They serve as a "sample" for the immune system to develop defenses against the pathogen. So, symptoms-wise, you may develop fever, headaches, fatigue, etc *due to the immune response* but nothing specifically in the airway dept because the virus is not reproducing. (The immune response is not localized in the usual tissue)

If it's the nasal spray vaccine, in that case it uses attenuated viruses (meaning live ones, but a strain that doesn't cause disease). Some people get a runny nose, but that's the closest to the flu-like symptoms you mention.