system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Does getting sick with the flu once provide the same effect as the flu shot for that year?

Basically, if someone got sick with the flu once already this year and then got it again a month later.  Does that first flu provide the same immunity effects against the second flu that a flu shot would have?
gpt
Kind of. You'll get immunity to that *particular* strain, but the flu shot typically contains vaccines against a few different strains. As such, you could still catch one of the other common strains that are going around, which the vaccine would have protected you against. 

Not all strains that go around are protected against by the vaccine, as sometimes the epidemiologists get it a bit wrong and chose the wrong strains. This is why having the flu shot doesn't guarantee that you won't then get the flu. 

Still, as the flu is horrible, it's worth getting the shot. They're cheap (or even free for many), virtually painless, won't give you the flu (you either already had the virus, or you've got a strain that isn't protected against). Definitely worth having. The flu can be particularly bad if you have certain medical conditions, like asthma, COPD, or anything that leaves your immunocompromised (amongst many others).