Hey, kinda glad I stumbled upon this I'm actually doing a PhD in immunology at the moment and my research has implications for vaccine development so I tend to keep a close eye on it at the moment this is a very general pathway for how a vaccine is developed and produced.
For simplicity I'm going to call the disease were looking at Disease A.
We decide to make a vaccine for Disease A. First thing we do is study Disease A to figure out what it does, that the cycle of an infection is like. At the same time we find people who have had Disease A and take samples from them. Once you have encountered a disease you will develop something called Immunological Memory. Basically these are cells that have lived through the infection and they "remember" the infection so if you ever encounter it again they react straight away and can clear an infection before you get sick. These are actually the kinda cells that I study.
We test the peoples samples to find what parts of Disease A their cells recognise. These cells can only recognise specific molecules on the Disease A so we figure out what part of the disease the body most easily recognises and then run with that.
We take those parts of the Disease A and smash them up basically, mix then with things called Adjuvents and this is basically cellular debris, they are very important they help kick start and immune response by prompting release of signalling molecules in the body that activate the immune system and tell the cells to react.
We then take these smashed up bits of Disease A and stick them in a test tube with some immune cells from normally a mouse, mouse models are used a lot in immunology because genetically they share around 99% of the same genes as our immune system. If we get good results and the cells are showing hallmarks of developing memory, note these aren't nerve cells like your brain, memory cells in immunology mean something else entirely. Its just what we use to describe cells that have seen the infection before, we then move on to mouse models.
Once we get past that we then inject mice with the vaccine, we measure if they develop memory by taking blood samples and testing the immune responses. Note mice are NOT injected with the virulent disease, we categorically CAN NOT DO THIS UNDER UN LAWS they are injected with a form of the disease which can not cause harmful effects - they normally knock out the gene that cause the disease to be harmful. We asses them for development of immunological memory and if we have good results we move on to clinical trails.
Note human clinical trials can take 10 years to complete! They are long and arduous process.
Phase 0 clinical trails involve looking at the pharmokinetics and pharmacology in the body - so how the vaccine is processed by the body. These are small groups given tiny tiny tiny dosages to make sure that it doesn't kill people.
Phase 1 clinical trials assess safety. Small groups of people <100 are given the vaccine to test for safety, establish side effects etc.
Phase 2 clinical trials involves establishing the efficacy of the vaccine - so does it work? A few thousand normally in the area where the disease if prevalent. The subjects will be tested normally for antibodies and other immunological memory markers.
Phase 3 clinical trials involve the final establishment of safety and efficacy, the trials are conducted again on a larger scale by other independent labs not affiliated with the labs that did the phase 2 trials. These groups are normally large 3K+
Vaccines that make it through phase 3 generally go on to be used as the general public, their safety, efficacy and benefits, optimal use are looked at through sales in the general population.
Generally patients are not exposed to the disease in the lab, we don't infect them with it to test the vaccine. Note though it depends, some diseases are very rare it's not worth creating vaccines as for them to be truly effective we need to vaccinate whole populations. Once we vaccinate a huge number of people in a population we break up the train of transmission of the disease and we reduce its ability to spread. So a few people who are not immunised or can not be (some have very weak immune systems and can not be vaccinated or they are allergic to components of the vaccine) are also protected though everyone else being vaccinated - we term that Herd immunity.
okay so you know...I'm so sorry thats so long but I hope its helpful.