Thanks for the interesting question.
According the Center for Disease Control, it is not possible to get
the flu from a flu shot. The flu vaccine involves injecting a number
of different strains of the virus into the patient. The various
strains of the virus are killed or inactivated prior to injection.
This is done through the use of various chemical agents such as
formaldehyde and beta propiolactone. Because the virus strains that
are being injected are inactive, there is no risk of contracting the
flu from a flu shot.
There are some minor and rare risks associated with the flu vaccine.
-Soreness in the area where the shot was given
-A low-grade fever
If these symptoms do occur, they occur shortly after the shot has been
given and last for a day or two at most.
Another risk that rarely results from administering flu shots is the
development of Guillain-Barré syndrome or GBS. This is a syndrome
that results in one out of every 100,000 patients. It is an illness
characterized by fever, nerve damage, and muscle weakness. The CDC
says the following about the relation between GBS and the flu vaccine:
"It is thought that GBS may be triggered by an infection. The
infection that most commonly precedes GBS is caused by a bacterium
called Campylobacter jejuni. Other respiratory or intestinal
illnesses and other triggers may also precede an episode of GBS. In
1976, vaccination with the swine flu vaccine was associated with
getting GBS. Several studies have been done to evaluate if other flu
vaccines since 1976 were associated with GBS. Only one of the studies
showed an association. That study suggested that 1 person out of 1
million vaccinated persons may be at risk of GBS associated with the
It is not possible to develop the flu from the flu shot since the
viruses used in the vaccine are rendered inactive prior to injection.
There is a possibility of some mild flu-like symptoms shortly after
the shot is received, however these symptoms are short lived and do
not develop into the flu.
For more information on the potential side effects of the flu vaccine
CDC Influenza Vaccine (flu shot): Questions & Answers 2002-2003
CDC: Prevention and Control of Influenza
How are Vaccines Made?
Safety of the Influenza Vaccine
flu shot risks
influenza flu shot virus
cdc influenza vaccine
flu shot faq
Hope that helps! Please ask for clarification if needed