There is some indication that exposure to some other coronaviruses may improve immune response to the pandemic one, but I think it's still a bit vague and undef

There is some indication that exposure to some other coronaviruses may improve immune response to the pandemic one, but I think it's still a bit vague and undefined. Since there are coronaviruses in circulation which cause colds, this is possibly true. It's not something to base public health policy around though! You are certainly right that we lack a lot of understanding, including about various kinds of immune response to the virus which is critical to developing an effective vaccine. The level of scientific activity around this one virus is utterly phenomenal though. I'd like to think this is going to be a defining moment for human medicine, but I fear it might turn out otherwise.