Imagine your body as an amazing castle; every castle has guards to protect what’s inside. That’s the job of your immune system: protecting against harmful attacks from organisms like viruses. The guards, our immune system, recognize harmful organisms and mount an attack. Immune cells eat the virus and spit out small pieces of it to other immune cells. This warns of the intruder, generates more immune cells, and specifies their attack. Looking back on 2020, we can see this isn’t a perfect system; sometimes our immune system needs extra help, either with medicine or a vaccine. What if those castle guards had the help of a secret messenger? One that warned them of the type of attack coming so they could better prepare for it? That’s how a vaccine works in our body.