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October 4, 2015 | by  | in Science |
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Shut up I love puns

In light of the rising numbers of “anti-vaxxers”, I’ve found myself immersed in far too many arguments where it becomes apparent that the opposition doesn’t actually know the mechanisms of vaccines. Here’s the simple explanation of the human immune system and how vaccines work.

The Immune System

The immune system is your own personal army, defending you against foreign invaders like unwanted bacteria and viruses. Non-“you” substances that invade the body are called pathogens or antigens.

The immune system can be described as having two “subsystems”, both of which are carried out by types of white blood cells: the Innate Response, and the Specific/Adaptive Response.

The Innate/Non-Specific Response

The innate immune system is the first line of defense. Innate immune cells recognise and respond to almost all pathogens, utilising a generic response—meaning they do the same thing to fight pretty much every pathogen they meet.

Upon exposure to a pathogen—for example, you cut yourself and bacteria enters your system—the cells at the site of infection release chemicals that attract your innate immune cells. These are called phagocytes (which literally means “hungry cells”). The two main phagocytic characters are called neutrophils and macrophages.

If some punk foreign cell like Billy the Bacteria attacks you, the cells that see Billy call out to Nancy Neutrophil and Marty Macrophage. They race over, and at first sight of Billy they race in and attack. Nancy Neutrophil performs phagocytosis, in which she essentially eats Billy and digests him. Sometimes Marty eats Billy; other times, Marty helps recruit the Adaptive Response to kill him.

Marty and Nancy don’t think things through much and essentially run in and go berserk whenever they’re called to an infection. They’re not very skilled, and no matter how many times they fight a particular enemy, they never figure out the most efficient way to kill it.

The Adaptive/Specific Response

Sometimes Nancy, Marty and the first-line furies are all you need to stop a foreign invasion. Other times they’re overpowered, so they recruit their more strategic buddies.

Two subtypes of cells called lymphocytes perform the adaptive response: B Cells and T Cells. Remember how I mentioned antigens? Every type of bacteria, virus, or other foreign invasion has different antigens. The adaptive immune response is described as specific because different B and T cells are “trained” to recognise one of these foreign antigens.

For example, when Marty and Nancy are having their phagocytic arses kicked, they call out to Helper T Cells. The Helper T checks out the antigens, allowing it to figure out what type of invader it is—for example E. Coli. Some Helper T Cells send messengers to the Killer Ts. These Killers travel the body searching for any of your human cells that have been invaded by the E. Coli. Even from inside your cells, they recognise the specific antigen and bind to the infected cell, activating it to self-destruct, killing the pathogen inside.

The Helpers send another messenger to stimulate the B Cells, which provide the basis of what we call Immunological Memory. B Cells are equipped with what we call antibodies, proteins designed to recognise specific antigens. Some B cells will be designed with an antibody to fight E Coli, some to fight salmonella, etc., etc. The Helper Cell messenger will activate the B Cells with antibodies for that exact infection.

However, sometimes your body doesn’t have the antibodies for a specific invader. When this happens, your T Cells and B Cells still help to fight, but aren’t as efficient. In this case, your B Cells spend some of their time studying the antigen on the invader and building the right antibody to fight it. After developing the required antibody, some B Cells head straight out to the battlefield. Others however remain floating throughout your body in a semi-active state, holding on to the new antibody in case you come into contact with this invader again: these are memory cells. Think about chicken pox—once you have it once, you tend to never get it again. This is because your memory cells formed the first time you fight it remember it, and if you’re exposed to it, they already know the most efficient and quick way to defeat it.


Thanks to this adaptive immune response, your body is much more efficient when fighting a disease it has already fought before—thus the premise for vaccines. Vaccines are designed to show your immune system something that looks the same as a particular pathogen, so it can how to fight it if you are exposed to it in the future.

There are different types of vaccines: Inactivated vaccines contain particles of a pathogen that have been grown and then deactivated/killed. Attenuated vaccines contain pathogens that are still alive, but have been weakened to make it far easier to kill. Subunit vaccines contain just the antigens of a pathogen, without needed to introduce the entire pathogen.

Why do we need new flu shots every year?

Much like animals adapting to the environment to survive, pathogens can do the same thing. Some are better than others, for example the influenza virus. The influenza virus is able to perform something called antigenic drift. As our bodies develop the ability to detect the antigens the flu virus has, the flu virus mutates over time, resulting in antigens different enough that our immune systems can no longer recognise them.

Regardless of the immune virus mutating, the immunity conferred from the influenza vaccine is often only short-lived, only protecting you for a few months.

How do I endanger others by not getting vaccinated?

The problem is not everyone is able to get vaccinated. That’s why you often hear about herd immunity. Sometimes regardless of being vaccinated, an individual’s immune system didn’t learn how to fight it well, and are still susceptible to a disease.  Other times, an individual may already be too sick with an alternative to disease to get vaccinated—this is an example of being immunodeficient. For example, young infants, the elderly, and individuals with cancer or HIV do not have strong immune systems. Even a vaccine made from deactivated particles can be too strong for their weak immune systems.

If everybody around them gets vaccinated, they have a higher level of protection—via herd immunity. For every healthy person that chooses not to get vaccinated, they are increasing the likelihood of exposure of a disease to those with a weakened immune system.

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