How does a vaccine work? What viruses are particularly difficult to design a vaccine for?

Biology/Immunity Vaccines

A: Thank you for this GREAT question from an awesome 6-year old follower. A vaccine takes a dead or very weak virus and introduces it to the body to trick your immune system into building an immune response that protects you. Viruses have antigens that work sort of like a name tag. When your body detects a virus, it builds new antibodies with B cells or finds old antibodies floating in your blood that match a specific antigen. The antibody binds to the antigen marking the cell for destruction. T-cells then come to destroy infected cells and remember how to get rid of that specific virus the next time you meet it.

Sometimes, viruses change quickly so that your body doesn’t recognize the virus. This lets the virus sneak in and make you sick. It’s hard to make vaccines for viruses that change quickly, like the flu. A trick around this problem is to include the most common strains of the virus in one vaccine. This increases the chance that the vaccine will protect you.

Antibodies, the tags that mark the virus for destruction before it makes you sick, last different amounts of time. Some stay with you for your whole life, like the antibodies that protect you from getting chickenpox again, while others can disappear after a few months. Making a vaccine for a virus with antibodies that only live for a short amount of time means the vaccine will only protect you for a short period of time. An example of this is the rotovirus, a common stomach virus that makes people barf and poop a lot. This vaccine only lasts about 2 years. For some vaccines, a vaccine booster dose is used to maintain the body’s immune memory and protection.

Viruses are smart and are always working to trick their way into the body. They use multiple disguises to get past the immune system. Scientists work to figure out the tricks of each virus to build new methods to stop it from entering the body and infecting our cells. HIV is a virus we still haven’t made a vaccine for. Scientists continue to study this virus and others, like the new coronavirus, to create new vaccines.

Check out this video featuring virus tagging, smashing, and disguises!

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