Let's see, the pandemic started in China at the end of 2019, since then it has been 7 months and has spread all over the world. If I'm telling you that the antibodies disappear in short periods ... there was more than enough time for this to be detected. I think it's too early to know what really works and what doesn't, this is something that will affect our daily lives for a while longer.
Here is an article that talks about people who lost their immunity
Many believe that we will only achieve immunity until some effective vaccine is found.this is a race that many seek to win.