So studies of other coronaviruses show immunity lasted 6-12 months. We’re a but early to see mass reinfections.

That said, my guess would be normal reinfections would be less severe, more like a cold. There have been some severe reinfections but any reinfection under six months suggests something atypical in the immune response.

Also SARS-Cov-1 produced a longer immune response so that may happen here.

But lifelong sterilizing immunity seems pretty unlikely based on what we know so far. The vaccines aren’t aiming at sterilizing immunity actually, their goal is to greatly lower the severity of the infection.

Studies also show that the immunity for original SARS (the close relative) lasts many years.

Yeah that’s what I meant by SARS-Cov-1. But I prob should have gone with the clearer term

Read the papers on it, antibody tests in people who have previously tested positive for covid have found little or no antibodies in tests taken 3 months after infection. So it appears as if there is a limited/short term immunity after initial infection. The vaccine appears to produce a much stronger immune response, such that antibodies can be identified in tests some time after the vaccination.

You can get limited immunity from the common cold after being infected but you are just as likely to catch it 12 months later anyway. With covid that means we are dealing with it annually, which our health services cannot keep up with.

There are more immune mechanizms beside antibodies (T-cells, B-cells). For the common cold there are different viruses, so you may get a cold caused by different ones.

antibodies disapear quickly, but the B-memory cells that produce them are still in the body ready to be mobilized.

"Common cold" and "flu" is not 1 virus, but hundreds of different viruses which is why you get them repeatedly. You do build immunity though. It's why children always have a cold and adults a lot less common.