SARS-CoV-2 is a new strain. Like going to the Ford dealer. Lot of Fords but they are all a little different. This one is the Bronco so to speak. Coronaviruses cause URIs this is not new. No one had immunity to this strain if you go back to ground zero day 1.
As one is exposed they will develop immunity. With this virus is takes about 5 days before your immune system starts kicking out antibodies. Antibodies attack the infection. After the infection you will have immunity to this strain. The more persons in the community that have immunity the less likely those in the community who aren't immune will get sick. Herd immunity.
I'm not on the hype bandwagon, SARS-CoV-2 for the older folks and those with comorbid conditions, this is the real deal. It's been shown to be especially hard on those with heart/lung conditions. Personally, I'm taking precautions to protect those at-risk.
They are testing, initial phases, vaccines. There is word there are some coronavirus antivirals on the horizon.