How do vaccinations work

[Yai]

How do vaccinations work - ie because your blood is constantly replaced, when a vaccine is injected, how does it stay in your system and provide protection against diseases ?

[Ewood27]

I'm sure someone will come up with a more technical answer, but as I understand it the vaccine doesn't stay. It is a weakened form of the disease and its job is to make your body produce antibodies to that disease, so that if that particular infection shows up, the defences are ready. The antibodies do stay.
To be pedantic, "vaccination" only refers to protection against smallpox (done with a cowpox culture - vaccus being Latin for cow). For other diseases it's an "inoculation". Same difference though.

[j2buttonsw]

I think the theory is that you have a whole gamut of different antibody producing cells always in your body that react against different "antigens". You use an attenuated (essentially broken) version of an antigen (eg the small pox virus) to induce the naturally occurring antibody creating cell for that antigen to start production antibodies. The trick being that once this particular antibody producing cell has been stimulated once into producing the antibodies it reacts quicker and more potently against the antigen if it is introduced a second time (in our example, if you were to be infected with the genuine smallpox virus).

[Jaybee]

There are also very few inoculations which give lifetime protection. 10 years seems to be the maximum, especially if the body doesn't meet the disease 'in the wild' so to speak and have the immune system stimulated to resist it. Some parents contract polio from the vaccine shed in their baby's nappy after inoculation despite having received the vaccine themselves. Smallpox immunity is also reputed to last about 10 years.

[mochyn]

The only thing I can add to the above fine answers, is that once the antigen (piece of bacteria/virus/fungus) is picked up by "scavenger" / Antigen Presenting Cells that are found all over your body, skin, mucous membranes etc - they are taken to immune organs such as the lymph nodes, thymus, spleen. They present the antigen (from the vaccine) to the T cells that reside there. The T cells will then become "activated", start to replicate, forming "Effector T" cells which fight the disease, but also "Memory T" cells. Its these memory cells that stay in the immune organs just hanging round waiting for the body to come into contact with the same antigen again. When that happens they start to divide rapidly into effector cells, so the infection is dealt with very quickly because the body doesnt have to "relearn" the second time!