FluMist . Flumist is an influenza vaccine given as a nasal spray. It differs from the traditional influenza vaccine in that it contains live, attenuated strains of influenza virus. These are weak virus strains that cannot cause disease. By contrast, the injectable influenza vaccine contains killed influenza virus or virus fragments. Both forms of influenza vaccine work by allowing your immune system to become familiar with the virus, so that protective antibodies are generated that prevent later infection with active virus. Theoretically, FluMist might give better protection against the flu because exposure is through the nose, which is the way most natural flu infections occur. Studies have had varied results; data suggests that FluMist gives superior protection to the injectable vaccine in children, but that the injectable vaccine is better than FluMist in adults. In all studies, the differences were small, and FluMist appears to be an effective option for adults and children. Flumist is recommended for healthy children and adults. It is not recommended for people with serious medical conditions or impaired immune systems, due to the remote chance that they could be made ill by the live virus. This has not been reported, but is theoretically possible. While unlikely, the live virus used in FluMist could be spread to others, so the injectable vaccine is preferred for those who have close contact with people who should not receive flumist.
Live/weak strains. They take the strains picked for the annual vaccine & weaken them to the point they cannot cause the flu. It is squirted up the nose & makes its way to the lungs where it causes a mild inflammatory response as it crosses into your blood to start promoting antibodies.This inflammatory effect in the lung makes it unsuitable for anyone with an asthma/lung conditions.