system
Given the following post, respond as if you're commenting on Reddit:
human
How does a flu vaccine lessen symptoms when you catch a flu variant that isn’t one of the variants in that seasons vaccination?
gpt
First, we have to understand how vaccines work, in general. The basic premise is, we take a virus/bacteria and break it down into large chunks. These chunks are the outer shell/wall of the virus/bacteria, and as with most other cells, there are proteins that are embedded into them for communication, transport, etc.

Second, we have to understand how the immune system works. There are two phases, the innate phase and the adaptive phase. The innate phase is the first line of defense. Your body recognizes something is foreign and tries to get rid of it. It knows this due to the proteins in the wall chunks, as they don't have "self" displays within them. Once they're cleared, your immune system will begin developing other proteins (antibodies) for the adaptive response in case of a repeat infection. If you get infected with the same proteins, your immune response is much quicker as the antibodies alert better killing immune cells to Ninja in and eradicate the problem.

The issue with the flu is that it mutates a lot. Changes to the DNA and RNA subsequently change the comms proteins on the viral/bacterial walls. It might change some greatly, some not at all, but the reality is, there are some antibodies hanging out that can still tag some portions of the cell for removal. They can't tag them efficiently, or in great numbers, but it reduces the viral load down to something more manageable by the innate system than if nothing at all. Your fever spikes, you feel like crap for a day or two, but by them time you've truly noticed it, your innate system has already turned the tide and is just killing off stragglers, all the while making more antibodies for the new proteins. The new antibodies begin circulating while you have the adaptive system out in great numbers already, so they begin to work quickly as well, further reducing your infective time.