To understand how vaccines and other pharmaceuticals work, we need to understand the immune system. You can think of your immune system like your own personal army protecting you from outside threats. With this in mind, the first term that we should define is pathogen: an agent that causes disease. These can be foreign bacteria, like Streptococcus pneumoniae, which causes pneumonia, or it could be a virus, like the Measles virus. Your immune system is designed to protect you from pathogens. Pathogens carry foreign proteins that are referred to as antigens and these antigens are what trigger your immune army to attack.
So who is involved in this very important immune army? The immune cells are called lymphocytes (aka white blood cells) and are made up of T cells and B cells (Figure 1). There is a difference between T cells and B cells in where they are produced and how they interact with antigens, but for simplicity, I am not going to delve into the differences. Both T cells and B cells work synergistically to create long term immunity. I am going to focus my explanation on B cells.
B cells produce and secrete little Y-shaped proteins that bind to antigens (Figure 2). These Y-shaped proteins are referred to as antibodies and are specific to a particular antigen. These antibodies then roam around your blood system and if they encounter the pathogen they are specific for, they will bind to the antigens on the virus or bacteria pathogen. This marks the pathogen for destruction. Large cells called macrophages will come along and eat the virus or bacteria cells marked with antibodies and destroy them.
Your Body at War: A Summary of Your Immune System
A foreign invader (a virus or bacteria) enters your body and makes you sick. Your immune system sends in its troops, the White Blood Cell corps, to fend off the invaders. The cells create and secrete proteins called antibodies that will mark the invaders. Then large cells called macrophages come along and eat the foreign cells that have been marked by the antibodies. After you’ve defeated the enemy, you keep the antibodies. The antibodies will then continue to patrol your body’s perimeter and if that particular invader tries to come back in, the antibodies will mark it for destruction before it can even cause disease.
How then does vaccination work?
The idea with vaccines is that you trick your immune system into thinking that it has the disease. You provide your immune system with the necessary antigens to create an immune response, but doesn’t provide it with the actual disease causing agent. Therefore you get an immune response but you don’t get sick. Your body will produce antibodies against that particular disease so that when you are exposed to the actual disease, your immune system immediately marks the pathogens and destroys them before they have a chance to make you sick.
I said above that your immune system usually wins, so why do we even care about this? Well, just because your immune system may win, it doesn’t mean that it does not suffer some losses. For example: measles, you may not die, but you may end up losing your hearing. Mumps: you may actually lose your ability to reproduce. Polio: you may be paralysed for life. And of course, you can actually die. The flu causes over 100 000 deaths world wide every year, and that doesn’t even count the millions who have died in massive flu pandemics prior to the advent of the vaccine.