These are the hot questions at the moment. It is the hope of everyone that if you do catch Covid19, you will be immune for a considerable time. On the one hand, immunity to the common coronaviruses that cause "colds" are not long lasting, so you can catch them again as soon as four months after recovery. On the other hand, immunity to SARS lasted for up to ten years. How will Covid19 compare?

Unfortunately, it seems that antibodies peak after a few weeks, and start declining after that.
https://www.sfchronicle.com/health/article/With-coronavir...

If antibodies do fall that quickly a vaccine will most likely not offer long term protection, either, so this may turn into something that people get every year, or a couple times a year. Let's hope not.

Antibodies are not the only measure of immunity, however. Our bodies have multiple defenses, including memory B cells and memory T cells. If these persist, they may have some effectiveness in minimizing and shortening the duration of re-infections. Memory T cells are of particular interest because SARS-COV2 shares many proteins with the common coronaviruses, with which we have all probably been infected with at some point. Thus, the memory T cells may recognize SARS-COV2 immediately, and help the body fight it off quickly, which may be why so many people have mild or asymptomatic cases. It may also explain why the case totals seem to go only so high before slowing down, rather than rapidly running through the entire population. No state or country has reported more than 4% infections, which is not what you would expect if this were truly a novel virus, to which no one had any defense.

So many questions, and so few answers. Treatment options continue to improve, but we still don't know the answers to some big questions. How long does immunity last? How soon can a person be reinfected? If a person is reinfected, will it generally be more mild, or more severe?