Is there any virus that when someone has natural immunity, that the someone can get it again? When the body fight the virus and won, the body has the code or the program installed in the body to win the fight again and again for this type, right? Or is there an expiration date on the program?

Who got the covid-19 virus and have natural immunity and never got the covid-19 vaccine and never was sick again with the covid-19?

We see know, the ones who got the mRNA covid-19 vaccine also got sick again with covid-19, right?