Live attenuated vaccines utilize a weakened form of the pathogen, whereas inactivated vaccines employ a killed or inactivated version of it.

Live attenuated vaccines are developed by reducing the virulence of a pathogen while keeping it viable or “alive.” This process typically involves cultivating the virus under conditions that impair its ability to cause disease but still allow it to elicit a robust immune response. A prime example of a live attenuated vaccine is the measles, mumps, and rubella (MMR) vaccine. These vaccines are highly effective and often confer lifelong immunity with just one or two doses. However, because they contain a small quantity of the live virus, they may not be appropriate for individuals with weakened immune systems.

Conversely, inactivated vaccines consist of viruses or bacteria that have been killed or rendered inactive through heat or chemical means. Since these vaccines cannot replicate, they are incapable of causing disease. The inactivated polio vaccine and the hepatitis A vaccine are notable examples of inactivated vaccines. While they are generally safer—since they cannot induce even a mild form of the illness they protect against—they typically provoke a weaker immune response. Consequently, multiple doses or booster shots may be necessary to establish and maintain immunity.

Both types of vaccines function by introducing the immune system to an antigen, which is a substance recognized as foreign. This exposure prompts the immune system to mount a response, including the production of antibodies. These antibodies provide immunity against subsequent infections by the same pathogen. However, the differences in the forms of pathogens used in live attenuated and inactivated vaccines can lead to variations in the strength and duration of the immune response.

In summary, live attenuated vaccines employ a weakened version of the live pathogen to generate a strong and long-lasting immune response, although they may not be suitable for all individuals. In contrast, inactivated vaccines utilize a killed or inactivated form of the pathogen, making them safer, but they may require multiple doses to achieve and sustain immunity.