I received a flu shot a few days ago. It's really been quite interesting to see how my symptoms have changed.
On a typical day I observe that my sinusitis symptoms and allergies are heightened. This is probably because I have been colonized with a pseudomonas strain for quite a while.
A day after receiving a flu shot my congestion in the ear was improved and my sinuses are slightly less inflamed. Pollen and mold counts could have been declined, but not enough to improve my symptoms for multiple days. The improvement has now lasted over 2 days. Don't get me wrong though - the colonization is still present. The only change in my treatment, diet or lifestyle - is receiving the flu shot - so I'm pretty sure the flu shot is a significant factor in improving my symptoms.
So why would this happen? I would speculate that the flu shot micro-organisms (which are dead) have distracted my immune system temporarily to focus on the "flu bugs" instead of on the pseudomonas colony. Sure, this is just a theory and my doctor is typically unable to speculate since I don't provide enough quantifiable and verifiable data that can be tracked (such as a bacterial culture).
This condition is unlikely to last more than a few days, but I still found it interesting and it's always a relief to have any type of symptomatic improvement.