The major Infectious points of the flu mutate rapidly. Hence, no long term immunity. That’s why an overall flu vaccine has been so difficult. The non mutating points aren’t what causes the immune response. Coronavirus in general mutate the unimportant parts, leaving the highly infectious points relatively stable. It’s kinda the opposite of the flu so to speak. There. Just hasn’t been any need to make an immunization because SARS and MERS burned out too quickly, and the common cold isn’t dangerous enough to invest the time and money in. This thing is different.
Now, wether or not that brings long term immunity, who knows. But as far as short to medium range immunity, it should be good to go.