Some people have big hopes for 2021. Hopes of returning to some form of what we once knew as normal: being with friends and family, eating at restaurants and even seeing shows.

Those hopes are becoming closer to reality as more people get the COVID-19 vaccine.

But how does a shot in the arm become immunity against the virus that swept the world?

For the vaccines currently approved and recommended by the CDC, the answer is in a single strand of genetic code.

Messenger RNA, or mRNA, essentially tricks the body into thinking the COVID-19 virus is already present and ready to invade. It lets the body develop a full defense against infection before any real threat is there.

We can think of it as security guards protecting a person’s cells. We know dangerous troublemakers are coming to wreak havoc, but there’s only one bouncer and that’s the immune system. Without the vaccine, it’s not prepared for the crowd that could show up at any time.

Enter: the vaccine.

It brings mRNA into the equation, which helps good cells disguise themselves as COVID-19. It triggers a sort of training exercise in the body where cells that look like dangerous coronavirus but are actually harmless, help the immune system prepare a whole army of bouncers.

When the day comes that those troublemakers arrive, the body knows what the bad guys look like, how to stop them, and has plenty of bouncers ready to take action.