In this study, the volunteers are getting the licensed seasonal flu vaccine to see if the jet injector works as well as giving the vaccine by needle and syringe. The seasonal flu vaccine that the researchers are using is called trivalent influenza vaccine (TIV). It is licensed in the US to protect people 6 months of age and older against influenza. Influenza is a virus that is also commonly known as the "flu". The flu is a serious illness that kills over 35,000 people per year in the US alone. The flu virus constantly changes and that is why people who are at risk for developing complications from the flu, such as children, the elderly, and people with underlying health conditions need to be vaccinated every year. Volunteers will receive the 2009-2010 annual seasonal flu vaccine called TIV either by needle and syringe or by jet injection. The researchers will compare the side effects and see how well the vaccine generates an immune response when given by the two methods.