Right here's an article on the subject of immunity.
https://www.statnews.com/2020/04/20...nity-and-antibodies-and-plenty-we-still-dont/
So...
If you had it and have recovered you WILL be immune for a certain amount of time. Up to 2 years for most viruses if you generated a lot of anti bodies to fight off the virus.
However as time progresses the number of these antibodies in your blood declines. (The cells gradually die and are removed by the bodies dead cell clean up squad).
So the two questions that follow are:
1. How long will antibodies persist in the blood? For those who were ill or very ill it will be at least 6 months, but what about those who produced very few antibodies because they were barely ill?
For SARS and MERS the antibodies hung around for 2 years. For Coronavirus they dont know and won't know for a long time.
2. Can the body generate new antibodies quickly if you get reinfected with the same or a similar strain reinfected you. This is the big question that WHO are so concerned about. Some viruses, like Small Pox barely change in terms of the keys they use to infect cells. Others like the common cold and flu are constantly changing.