[twomoretime]

>they universally believe that immunity is real and at least moderately long-lasting

I haven't seen a single publication to this effect and there's no way to no for sure until enough time has elapsed to verify. Viral immunity varies widely and though it is in the coronavirus family it is still a novel pathogen.

[SpicyLemonZest]

There's no way to know anything for sure, but it's been experimentally confirmed that animal analogues can't be reinfected and that the antibodies people produce are effective against the virus. Remember that this is an emergency situation; we can't just wait and see, we have to work as fast as possible towards addressing the problem.