Assuming the immune system is healthy,
How much SARS-CoV-2 virus (cause of COVID-19) is required to make a person sick?
This might also depend on time, if it was a high infectious dose but just some minutes, maybe not that bad outcomes.
Or if it's a very low infectious dose, but during a whole day, maybe a bad outcome.
In addition, Would it be possible that a person was exposed to SARS-CoV-2 virus, and so the virus got inside their system, and even still this person's immune system didn't let the virus to infect this person?
Note that it's not the case that this person will be totally asymptomatic, it's the case when the virus wasn't "strong enough" to infect this person even being inside their system.
- MID - minimum infectious dose defined as"the smallest quantity of infectious material that regularly produces infection"