Welcome
Hi guys! I'm going to start out by stating that I do have an absolute bias about vaccines. I believe that vaccines, unless physically harmful for patients (i.e. those with compromised immune systems), should be administered to everyone. Socially, I do not believe that the world should be reduced to the way that it was 100 years ago, where people died of smallpox and measles. That being said, I will do everything in my power to maintain both my composure and scientific standing and remain (mostly) unbiased about what is published. So, welcome to Vaccine Vaniloquence, I hope you enjoy!
A BRIEF HISTORY
Vaccines (and their archaic predecessors) have been around since the 17th century, especially in China. Since the plague, smallpox had been a reigning infectious disease throughout the world, and the Chinese used blood transfers between bovine with cowpox (the cows literally had cowpox) and humans (think "blood sisters" from middle school) in attempt to gain immunity from the disease. Although the effectiveness of such is questionable, it showed an understanding of the immune system, and boosting it through outside influence. In terms of modern vaccinations, Edward Jenner is known as the father of vaccinology after doing the same (but scientifically!) in 1796, producing a mass movement and actual vaccine in 1798, according to the Immunisation Advisory Centre, based in New Zealand. Due to the early implementations of the vaccine, the disease was eventually eradicated in 1979! Vaccines gained a lot of ground with the development of the polio vaccine in 1950, and the subsequent eradication of the disease in many countries soon followed. Due to the (denounced) research of Andrew Wakefield, proposing a connection between vaccines and autism, as well as the use of small amounts of formaldehyde as a preservative, there has been a large social movement to stop all vaccinations in children, creating a large social disparity between scientists and the general public and a disbelief of the sciences as a whole that has yet to recover.
SO HOW EXACTLY DO THEY WORK??
(Most) every living being on Earth is born with an immune system that is strengthened with exposure. Viral strains have specific markers on the outside of their shell/cell membrane, called antigens. When the infection is introduced and overcome by the immune system, a specific cell (called a memory cell) within the immune system is modified to detect the specific antigen and fight it, using the white blood cells to engulf the intruder. Vaccines expedite this process by introducing the disease manually, instead of allowing the body to come across it naturally. The risk, obviously, is that the disease will compromise the immune system, instead of allowing it to adapt. To reduce this, a "dead" version of the strain is introduced, at smaller concentrations than would be found naturally, to allow the immune system to mark the antigen, and thus more easily overcome it when it is introduced. Those that do not have a functioning immune system (i.e. those undergoing chemo, AIDS patients, or those with autoimmune disorders) must then rely on a phenomena introduced by vaccinations: herd immunity. This is a sociological circumstance where, if a majority of the population is vaccinated (and thus immune) from a specific disease and strain, then the probability of an unvaccinated person getting infected is lowered by the sheer number of immune population surrounding them.
SO THERE YOU HAVE IT
If you want to read more about this topic, here are some helpful links:
http://www.immune.org.nz/vaccines/vaccine-development/brief-history-vaccination
https://www.niaid.nih.gov/research/how-vaccines-work
