To be clear, it also reduces your risk of infection.
macroscopically that can look like prevention of infection.
50% is a lot from a public health perspective -- there's a huge difference in the exponent -- but not something you can rely on to keep yourself or your relatives safe.
I agree that it’s waning, and likely boosters will help, but it is far better (and safer) than doing nothing; just doesn’t preclude the need to mask up around unvaxed folks, etc.
Note: Before anyone jumps on the above statement, I'm not trying to imply anything else. Vaxed folks who don't take reasonable additional precautions ARE a major source of spread COVID19. That's not meant as a comparative statement (unvaxed folks are ALSO a major source of spread).
Nevertheless, vaccines do significantly still reduce your risk of infection. Agreed on the rest.