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  • Vaccines are designed to protect you from a virus, and the way that they succeed is

  • by getting the immune system all worked up.

  • But this is exactly what causes those unpleasant side effects that can knock you off your game

  • for a day or two.

  • So, while the fatigue, headache and low grade fever are no fun, they can actually be proof

  • that the vaccine is doing its job and doing it well.

  • Your immune system is actually already quite good at getting rid of viruses but it isn't

  • all knowing, and when it encounters a new virus like the one that causes COVID-19, it

  • needs to be taught some new tricks.

  • And the best way to do this is through a vaccine that tells your body what to do if it encounters

  • the virus, essentially creating what's called a memory response.

  • Now everybody responds differently to a vaccine or an infection.

  • And so everybody's memory response is a little different, but the vast majority of people

  • their memory response is so fast so strong that it clears that infection from that virus

  • before it really has a chance to get established.

  • And so you won't have any symptoms, you won't even know you're infected.

  • Hi my name is Rick Kennedy.

  • I'm a professor of medicine at the Mayo Clinic.

  • I'm an immunologist by training, I study vaccines and infectious diseases, and I run the vaccine

  • research group here at Mayo Clinic.

  • So creating a memory response to a virus is key.

  • But how exactly does a vaccine do this?

  • Well, it might help to start with an understanding of how the immune response works.

  • The first part of the immune system

  • is called the innate immune system.

  • It's sort of your first line of defense.

  • It has three main jobs; the first job is to recognize that you're infected and sound the

  • alarm.

  • The second job is to try and recruit white blood cells and send them to the site of infection

  • to try and slow it down.

  • And then the third and probably the most important thing is to take the virus or the bacteria

  • that's infecting us and take it back to the rest of the immune system so that it can learn

  • to recognize and then destroy it.

  • The innate immune system fires up as soon as the virus gets into the body,

  • and it's that flood of immune activity that can cause symptoms like fever or muscle aches.

  • It sets the stage for the next phase of response, the adaptive immune response.

  • T cells and B cells are part of what's called the adaptive immune response.

  • So the first part of that are B cells, they're basically antibody factories, and each B cell

  • is specific for one little piece of one viral protein and that's called an epitope.

  • The antibodies produced by B cells will bind to this epitope and can block the virus from

  • attaching to or entering cells, they might be called B cells but they're really the A team.

  • Then there are the T cells.

  • Those are important because once a virus gets inside your cells,

  • the antibodies can't get to it, so it's hidden from the antibodies and it's going to turn

  • that cell into a virus factory and produce more viruses, that's how the virus spreads

  • through your body. You have killer T cells and helper T cells.

  • The killer T cells hunt down and kill infected cells, and yes

  • you guessed it helper T cells, help them.

  • You want to have both a strong innate immune response, and a strong adaptive immune response

  • to fight a virus, so every vaccine needs to have ingredients that trigger both.

  • Vaccines have two main components at least from the perspective of the immune system.

  • There's the part that would stimulate the innate immune response and that's called an

  • adjuvant and that's typically a molecule or a pattern that's found in a virus or bacteria

  • that's not present in humans.

  • When you're injected with a vaccine and the innate response is triggered, that's where

  • a lot of those well known symptoms come in the burst of activity to the site of the vaccination

  • is why your arm gets sore after a shot.

  • The other component is the antigen.

  • And that's really the piece that we're trying to have the T cells and the T cells target

  • and respond to.

  • So no matter which vaccine you get, you're getting a mixture with an antigen and an adjuvant

  • injected into your muscle cells,

  • There's some specialized cells called antigen presenting cells, they act like garbage disposals

  • and trash collectors, they just sample the environment so they will see the antigen and

  • pick it up, they'll see the adjuvant and say oh, something's wrong here, and then they'll

  • carry the antigen, to the lymph node. Lymph nodes are basically like a shopping mall,

  • T cells and B cells are coming in and out all of the time, and every T cell and every

  • B cell is looking for that one shirt on the rack that one epitope, that one piece of

  • the viral protein that it recognizes.

  • This process happens in the first few days as the B cells learn to make antibodies and

  • T cells learn to kill cells, or how to help kill cells.

  • They're also proliferating, growing and dividing and making clones of themselves because you'll

  • need an army of these white blood cells to fight off the army of viral particles that

  • is present in your body and infected, and that whole process takes about a week or two.

  • Now for an infection that's where the story ends, but for a vaccine, you're really not

  • trying to protect you against the vaccine you're protecting against a future infection.

  • Your body clears the antigen and the innate response calms down, then most of the T cells

  • and B cells will die off as their services are no longer needed, but some of them will

  • change into memory cells.

  • Memory cells will last for years, sometimes decades, they just circulate through your

  • body and they're fairly quiet until you run into that virus again.

  • Now, a naive cell the first time it sees antigen and it's learning to do its job, it's a little

  • bit like an infant taking its first steps, a memory cell, it's the equivalent of an Olympic

  • caliber athlete, it takes off running at full speed and it's fast, so the difference

  • between your memory response, and that initial response is that the memory response is 100

  • sometimes 1000 times stronger.

  • Okay, sign me up for these Olympic caliber cells ASAP.

Vaccines are designed to protect you from a virus, and the way that they succeed is

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