That's...not how a virus works. There's no "minor exposure" to build an immunity - you get exposed, you're exposed. If you get infected, with this one there's a chance you might be asymptomatic, but there's no guarantee - you're just as likely to wind up in intensive care on a ventilator. This thing is a virus no human has ever had until the last few months - we have no immunity until we fight off the infection, if we're one of the ones who can. So far, the percentage of the infected who fail to fight it off and wind up dying is much larger than comparable viruses. Plus, with it being communicable for 14 days before symptoms appear, it's much much easier to spread than comparable viruses. What you're reading on this is akin to trying to build up an immunity to gunshot wounds by shooting yourself repeatedly with a .22...it's just not realistic or any kind of good idea. This part appears to be somewhat accurate - but I wouldn't bet my health on it. What I've read says type O individuals are "less likely" to develop severe symptoms. That sounds like a crapshoot to me.