Before we talk about how vaccines work, we need to understand what immunity is.
Our immune system can recognize foreign invaders, also called an antigen, and produces antibodies against it. The first time the body encounters an antigen, it can take several days for your body to produce antibodies, and you will get sick. But the antibodies will remain in your bloodstream, and if the same antigen tries to infect you again, the antibodies will prevent you from getting sick.
How does the vaccine work?
Vaccines are made from the same antigen that causes disease, but the antigen in vaccines are either killed or weakened so they won’t make you sick. When the vaccines are introduced into your body, your immune system will produce antibodies. When the real antigen infects your body, the antibodies will prevent you from getting sick.
How to develop vaccines?
Vaccine development is usually divided into four phases: research and discovery, pre-clinical, clinical trials, production and marketing. The whole process could take up to 10 years.
During the research and discovery phases, researchers need to isolate the pathogen that causes disease. Then the pathogen will be treated in different ways so that they don't cause disease but at the same time stimulate the body to produce antibodies. These completely or partially inactivated pathogens would be a candidate vaccines.
During the pre-clinical phase, the candidate vaccines will be injected into animals to learn how it works, and how does it affect the body.
During the clinical trials, the vaccine will be injected into the human body. Based on the number of people tested, this stage is divided into three small phases, called phase I clinical trials, phase II clinical trials, phase III clinical trials.
All information and data collected during the development and testing of new vaccines will be submitted to the relevant regulatory authorities for review. If approved, the candidate vaccine can move on to the next phase.
Are there any bottlenecks to develop vaccines?
The vaccine development pathway is long and expensive. Almost every step has a bottleneck. I think the major bottleneck is clinical trials. During the research and discovery stage, Researchers will select several vaccine candidates, but often only one or none candidates will pass phase III clinical trials.