Right, this post will be about the very fundamental reasons for the success of vaccination as a procedure to prevent infections and epidemics of infectious diseases. Before we get started I want to introduce you to one or two terms that will be used in the remainder of the article, the first one is antigen, and the other one is pathogen. Pathogens are things like viruses and bacteria and in some cases toxins that cause disease, antigens are things the body uses to recognize things like pathogens (and other foreign bodies too, but that is not of consequence to this post)
Then of course we have the other part of the equation, the Immune System, which works to get rid of foreign bodies, these bodies being bacteria viruses et cetera, from the body, the functioning of the immune system, which mounts an immune response, can be arbitrarily divided into two parts, a nonspecific immune system (which produces innate immunity and does not distinguish between what foreign bodies it encounters) and an adaptive immune system (which is specific to the antigen and is acquired)
Acquired how? One might ask, well, to cut a long story short, phagocytotic cells digest a pathogen and present bits of it on their surface coupled to MHC proteins, other cells of the immune system process the antigen and this triggers the production of B cells which produce antibodies and T cells which facilitate a cellular response to said antigen specifically, thus allowing the body to get rid of the antigen.
However, doing all this takes some time, ranging from at least two days to two weeks, so if a pathogen gets into the body it can cause disease in that period, before the immune system is able to clear the inection out. If the person survives the infection, the primary immune response that had been induced in the aforementioned timeframe then leads to the establishment of immunological memory (the immune system basically ‘remembers’ the pathogen, the next time the same pathogen is encountered, the immune system is ready to get rid of it extremely rapidly, and this is why most people (those with normal immune systems) don’t get infected by the same pathogen twice, this secondary response is called, um, a secondary response.
The next question when one is looking to prevent disease is to ask if one may somehow prime the immune system against the pathogen so that the first encounter with the pathogen triggers a secondary immune
response…and vaccines do this, here is how…
1) Various things that belong to a pathogen can trigger an immune response, such as proteins on the surface and polysaccharide capsules.
2) These antigens can trigger immune responses without causing disease, as long as they are disjunct from the pathogenicity of the organisms.
3) By supplying antigens to the immune system without the risk of associated pathogenesis, it can be taught to recognize those antigens and mount an immune response against the antigens, and the pathogens that have those antigens.
This is just a very brief introduction for laymen to the world of vaccines, in the near future you may expect to see various posts on the nitty-gritties of this critical field of medical science.