You can't get Influenza from a flu shot, unless it's the nasal spray flu vaccine. The flu "shot" a killed virus and it cannot give you the illness. You may get some side effects such as weakness, a low grade fever and mild symptoms for a day or two, but you cannot get the actual strain of Influenza they are vaccinating for.
The nasal vaccine is a weakened live virus, and honestly, I wouldn't recommend it for anyone. The risks are higher than the benefits. I also don't like that this nasal vaccine was developed for children so that the safer killed injectable vaccine could be "saved" for seniors. Kids, if they are in day care or prone to respiratory illness and their parents choose to vaccinate them against Influenza should be able to get the same quality vaccine that adults, particularly senior citizens get. Why risk kids' health to save the vaccine for others. It should be available and first come first serve, with YOUNG people who have respiratory problems getting first pick of the injectable vaccine.
Any strain of Influenza is active any given year. The vaccines do try to cover more than one, but once in a while they miss the big one that year. But, the rate at which they DO get the right strain is higher than 30%!
That being said, I'm not getting one. We have used them in the past, when two of my three kids and myself got pneumonia from Influenza one year and our little one missed nearly 10 weeks of school. The next two years our "Ground Zero Patient" (the one daughter who always gets it first and brings in into the house) was vaccinated. But, we don't use flu vaccines on a regular basis.