If you do a search of vaccinations or Flu shots you will get more specific answers to your question.
Unfortunately I don't think there is one answer to your question. It probably varies with the shot and the individual. In general, though, my flare ups are of a much shorter duration than the original one, which went on for about a year. I think the fact that my anxiety is much less is key in having things calm down more quickly, usually just a few weeks. The more worried, the more twitches. There definitely is a correlation.
Remember, this too shall pass.
I have chosen not to get Flu shots anymore. I realize I may feel badly about that choice if I come down with a bad flu, but for now I feel I don't want to give my immune system anything more to try to figure out.
Take care.
Beth