Live attenuated versus Inactivated vaccines

Two forms that a vaccine can take is either a live attenuated vaccine or an inactivated vaccine. Inactivated vaccines are typically not as effective as a live vaccine and are created by inactivating viral or bacterial components and introducing them to the immune system.  These vaccines do not replicate inside of the body since the organisms are not alive, and they are not affected by circulating antibodies. Unfortunately, these inactivated vaccines do not illicit a strong immune response, and thus can require up to as many as five doses and boosters to remain effective.  In addition, the patients’ antibody titers can diminish over time.

Live attenuated vaccines are considered a weakened form of the normal infectious agent, be it a virus or a bacterium. The strains are typically weakened in a lab over a series of repeated culturing. Unlike inactivated vaccines, live vaccines do require replication within the body to illicit an immune response, and thus can be negated by circulating antibody. The measles viral vaccine is particularly susceptible to this type of failure. Importantly, due to the live nature of the vaccine, the vaccine can be damaged by certain agents such as radiation or heat before it is administered. They must be handled and stored very carefully to avoid a failure in the vaccine.  Other than live vaccines that are administered orally, these vaccines are typically effective with a single dose.  Immunocompromised patients should be wary of receiving a live attenuated vaccine due to the replicative mechanism of action.

Additional Source: http://www.immune.org.nz/types-vaccines