All you have to do is look at HIV or the Spanish Flu. They didn't kill their infected as much as they compromised immune systems and opened people up to all kinds of serious infections. Pneumonia was common among those who had the Spanish Flu. Apparently you want it to be some mysterious slow moving virus that will get us eventually. Just a matter of time now. It's mid-2022, more than two years after covid started spreading like wildfire here. If it did, as you say, compromise immune systems we would be seeing that big time. As in more deaths here and around the world than covid itself. But that wouldn't make for a very exciting conspiracy theory now would it?