Don’t be too quick to jump to conclusions. There is a good possibility that when you were vaccinated, your immune system was already in a weakened state—conversely, it might have been slightly hyperactive, common among young adults.
In a weakened state, being vaccinated might have stressed it further, making you susceptible to acute viral nasopharyngitis, aka “colds”, and other URTIs, which may have been dormant in your sinuses, then activated. People are loaded with such pathogens (even MRSA and NF, the “flesh eating bacteria”) are commonly there, as idle, opportunistic threats.
Conversely, if your immune system was a little too active, it would easily overreact to the introduction of the antigens in the vaccine, treating it as if it was a new and deadly flu, which it isn’t.
Flu vaccines are usually created like this. In the name of a particular flu, say “H1N1”, the “H” factor is how the viruses enter human cells, and the “N” factor is how they get out again. Each of these factors has 8 gene segments. Scientists slice off two of the H, and two of the N gene segments, and splice them onto a different kind of virus genes that affects chicken, but not people.
When this is injected, your immune system spots those 2 out of 8 H gene segments, and 2 out of 8 N gene segments, and creates antibodies to fight any virus that has those 4 segments. Otherwise, the chicken virus just sits there and doesn’t infect you.
However, a hyperactive immune system might misinterpret the harmless chicken virus as a new and lethal threat, so the immune cells and the chicken viruses duke it out in your lung tissues. Hence the severe bronchitis.
Immune systems tend to settle down after the age of 40, so are much less likely to get such “false positives”. So if you got such a reaction to a flu shot when younger, it may no longer be a problem if you are over that age.
Cheers!