A quick hit on the dose-response.
"Dose-response
Since the beginning of the pandemic, several animal studies looked at the dose-response relationships for symptoms, seroconversion and viral shedding through orotracheal [140], intranasal [141] and aerosol [142] exposure. Most recently, a human challenge study enabled the identification of the Median Tissue Culture Infectious Dose (TCID50) or the inoculum dose that induced infection in more than 50% of participants, corresponding to 10 TCID50 or 55 Focus-forming Unit (FFU) [143]."
What the heck is a focus-forming unit you say?
"A measurement of the concentration of live virus in a given amount of fluid. This is measured by spreading a known amount of the fluid over a layer of cultured cells which are infected by the virus, then counting the number of areas in the culture which look infected."