In order for natural immunity to occur, it involves 2 different types of antibodies. For those that are curious as to the science behind this, I found my notes from immunology class in college and will post some of them and explain it more below https://twitter.com/who/status/1253999800221085696

When a virus first attacks the body, the IgM antibody is produced. This antibody remains in the body for up to 4 months, but reinfection/secondary immune response can still happen during that time. This is where the IgG antibody is formed (see below for differences)...

At that point, secondary IR usually lasts a shorter amount of time than primary IR (see picture). IgG antibodies have a longer half-life (~25 days), and these are the ones that remain in the body for life. This is where you have natural immunity because a certain white cell...

...known as lymphocytes produce antibodies that will be released when the body detects the antigen.
Disclaimer: it’s still too early to tell whether COVID-19 will follow this trend so I’ll leave that to the virologists to research that. Hope you enjoyed this little science lesson