80% of those infected have no symptoms or have mild symptoms.
Impossible to track or contain.
You've nailed it, at least in the sense of sustained containment.
There is a crude analogy to alcohol. Most people can and do drink alcohol, usually self-limiting themselves to moderate amounts, usually not doing themselves undue harm, and not getting addicted to it or showing any sign of addiction. A much smaller % reacts completely differently, becomes addicted, and does great harm to themselves and others.
The difference is that non-alcoholics usually don't "infect" alcoholics in the usual sense of the word "infects". But, we "normals" do generally insist on some freedom of alcohol availability, so maybe we do cause "infections" after all. ??