There's some very strong indicators that immunity will be ephemeral.
It's possible the R naught will drop below the currently assessed 2.2 over time, but there's no evidence for that -- and if both these things stay as expected, it won't be transient enough to 'die down' naturally.
Unfortunately until we get an antigen test, we will not know for sure. But there is no reason to believe at this point that it isn't anything other than a standard immune response.
There is no evidence either way. Even if it is transient it will be enough for it to die down