Flu Shot, (Influenza Vaccine) is an annual vaccine to protect against the highly variable influenza virus. Each injected seasonal influenza vaccine contains three influenza viruses: one A (H3N2) virus, one regular seasonal A (H1N1) virus (in 2010 this was replaced by the 2009 pandemic H1N1 virus), and one B virus.Comparing flu shot to nasal spray Flu vaccines are available either as: TIV (flu shot of trivalent (three strains; usually A/H1N1, A/H3N2, and B) inactivated (killed) vaccine) LAIV (nasal spray (mist) of live attenuated influenza vaccine.) TIV works by putting into the bloodstream those parts of three strains of flu virus that the body uses to create antibodies; while LAIV works by inoculating against those same three strains that have been genetically modified to minimize symptoms of illness. LAIV is not recommended for individuals under age 2 or over age 50, but might be comparatively more effective among children over age 2. Various public health organizations, including the World Health Organization, have recommended that yearly influenza vaccination be routinely offered to patients at risk of complications of influenza and those individuals who live with or care for high-risk individuals.