I've heard from virologists that the amount of virus you're exposed to does matter. A gallonful of virus can quickly overwhelm the immune system, a small amount

I've heard from virologists that the amount of virus you're exposed to does matter. A gallonful of virus can quickly overwhelm the immune system, a small amount can take long enough to grow that your immune system can ramp up to deal with it before it overwhelms. It's like someone releasing one breeding pair of rats in your attic vs 100. I don't have a cite, it was from the "This Week in Virology" podcast. I also heard a number going around suggesting that an early group of people hospitalized and killed were Ear, Nose and Throat doctors, who obviously would have been exposed to an almost comically large amount of the virus. Giving someone a little bit of smallpox was a known immunization method before modern methods were invented. You'd still get sick, but less sick, and you'd wind up immune. https://en.m.wikipedia.org/wiki/Variolation https://en.m.wikipedia.org/wiki/Variolation