Thew whole idea is fascinating and there are also a limited number of real world studies (aka trying to infect people with live virus) to chose from. Influenza

Thew whole idea is fascinating and there are also a limited number of real world studies (aka trying to infect people with live virus) to chose from. Influenza seems to have a threshold. If the dose is too low people don't get sick. At the threshold you see some people get sick and some people develop antibodies without symptoms.