I did not know that I had CFS for years. I did know that my ongoing health problems were the aftermath of a horrific case of the flu. I was determined not to get the flu again and began taking flu shots at that time. My reaction is very predictable. Twenty-four hours after getting the shot, I get a reaction that lasts twenty-four hours. I have not had one the last few years partly from reading that some people thought it was a bad idea for those with compromised immune systems and partly because I now live in a rural area where it take more time and effort to get one. I am also leading a lifestyle (semi-hermit) that is less likely to expose me to the flu.