Why am I feeling fatigued after getting my flu vaccine?

What about people who get a seasonal flu vaccine and still get sick with flu-like symptoms?
There are several reasons why someone might get flu-like symptoms even after they have been vaccinated against seasonal flu.
You may also read:
Egg Allergy and Flu vaccine : egg free options are available in Europe but not in USA in 2011
Latex Allergy : some needle tips are coated with latex, eg., intradermal delivery of flu vaccine. Please, confirm about absence of latex coated needle tips on package insert. See video on Intradermal Flu vaccine technology  by Fluzone  microneedle, the first intradermal flu vaccine approved using the microneedle technology and available for 2011-2012 flu season.

A Flu Virus

The Centers of Disease Control lists the following common reasons for feeling unwell after getting the flu vaccine:

1. People may be exposed to one of the influenza viruses in the vaccine shortly before getting vaccinated or during the two-week period that it takes the body to gain protection after getting vaccinated. This exposure may result in a person becoming ill with flu before protection from the vaccine takes effect.
2. People may become ill from non-flu viruses that circulate during the flu season, which can also cause flu-like symptoms (such as rhinovirus). Flu vaccine will not protect people from respiratory illness that is not caused by flu viruses.
3. A person may be exposed to an influenza virus that is very different from the viruses included in the vaccine. The ability of a flu vaccine to protect a person depends largely on the similarity or “match” between the viruses or virus in the vaccine and those in circulation. There are many different influenza viruses. For more information, see Influenza (Flu) Viruses.
4. Unfortunately, some people can remain unprotected from flu despite getting the vaccine. This is more likely to occur among people that have weakened immune systems or the elderly. However, even among these people, a flu vaccine can still help prevent complications.

Seasonal influenza vaccine provides the best protection available from seasonal flu—even when the vaccine does not exactly match circulating seasonal flu strains, and even when the person getting the vaccine has a weakened immune system. Vaccination can lessen illness severity and is particularly important for people at high risk for serious flu-related complications

Dual flu infections: Australian scientists have discussed a “dual flu infection” phenomenon reported by Japanese scientists in 16 students. 1) They reported that vaccination with the regular flu season vaccine resulted in a higher risk of infection with H1N1 and they give their scientific opinion on why that happened in some areas of the world and not in others. 2) They hypothesize that a strand-transcending short-term immunity results. In other words, it is usually rare that two strains of influenza A attack in the same year and so close to the infection by the other strain. If the second strain attacks quickly after the first strain infects, then there is some transient immunity which protects; however, longer this gap this immunity wanes. So, by their theory, dual infections have a gap.Super immunity: This is the “holy grail” of flu scientists – to discover the one vaccine that will prevent all strains of flu. Apparently, natural survivors of the H1N1 infection may have a “super immunity” to all known Influenza A strains of the flu virus. A BBC article. describes Dr Patrick Wilson and his colleagues work on this. In my opinion, lets see what happens in the next few flu seasons.However, scientists caution that a vaccine developed to achieve similar “super immunity” results will have to undergo several years of clinical trials before being eligible to be marketed.