That is misinformation. There is no reliable scientific evidence that natural cellular immunity will wear off. You might be confused by antibody levels, which are relatively unimportant.
These are an older article so not sure if there is something more recent. https://www.cdc.gov/coronavirus/2019-ncov/your-health/reinfe... https://www.cdc.gov/coronavirus/2019-ncov/your-health/about-...
It was also my understanding that recovery from one varient does not necessarily provide protection from a different varient. And also infection is not cut and dried and influenced buy duration, viral load and many variables.