How do vaccines differ in live attenuated and inactivated forms?

Live attenuated vaccines use a weakened form of the pathogen, while inactivated vaccines use a killed or inactivated version of it.

Live attenuated vaccines are created by reducing the virulence of a pathogen, but still keeping it viable, or "alive". This is often achieved by growing the virus in conditions that disable its ability to cause disease, but allow it to still stimulate an immune response. The measles, mumps, and rubella (MMR) vaccine is an example of a live attenuated vaccine. These vaccines are very effective and often provide lifelong immunity with only one or two doses. However, because they contain a small amount of the live virus, they may not be suitable for people with weakened immune systems.

On the other hand, inactivated vaccines use viruses or bacteria that have been killed or inactivated with heat or chemicals. These vaccines cannot replicate and are therefore unable to cause disease. The inactivated polio vaccine and the hepatitis A vaccine are examples of this type. While inactivated vaccines are safer, as they cannot cause even a mild form of the disease they are protecting against, they generally stimulate a weaker immune response and may require multiple doses or booster shots to maintain immunity.

Both types of vaccines work by presenting the immune system with an antigen, a substance that the immune system recognises as foreign. This stimulates the immune system to produce a response, including the production of antibodies. These antibodies then provide immunity against future infections with the same pathogen. However, the difference in the form of the pathogen used in live attenuated and inactivated vaccines can result in differences in the strength and duration of the immune response.

In summary, live attenuated vaccines use a weakened form of the live pathogen to stimulate a strong and long-lasting immune response, but may not be suitable for everyone. In contrast, inactivated vaccines use a killed or inactivated form of the pathogen, are safer, but may require multiple doses to achieve and maintain immunity.