There is a sublinear aspect actually, which is easier to see (because it is a larger effect) for large risks. So lets say you do two 100,000 microcovid (or 10% chance of catching covid) events. Your chances of not catching covid from one event are 90%, so your chances of not catching covid from either event are 90% * 90%, or 81%. So your chances of catching covid from at least one of these events is 19%. 100,000 microcovids + 100,000 microcovids = 190,000 microcovids. The arithmetic we do of adding microcovids by the ordinary rules of arithmetic is a good approximation for relatively small numbers of microcovids, but the actual addition of the risks is sublinear, it does not follow normal arithmetic.
That said, in principle I think you are right that two covid-inhaling events close enough in time will add in a superlinear way for biology reasons. That could be, as you suggest, getting a worse case of covid. It could also be catching covid, when neither event was bad enough on its own to do that. Lets say the threshold to be infected is 100 virus particles (I have no idea the actual number), and each event gives you 75 virus particles. If they happen far enough apart, you don’t get covid, but if they happen one right after the other, you do get covid. Overall, I expect this effect to be small. Unless you are doing super risky things, or working in the covid ward of your local hospital, you probably aren’t encountering two infected people right in a row.
There is a sublinear aspect actually, which is easier to see (because it is a larger effect) for large risks. So lets say you do two 100,000 microcovid (or 10% chance of catching covid) events. Your chances of not catching covid from one event are 90%, so your chances of not catching covid from either event are 90% * 90%, or 81%. So your chances of catching covid from at least one of these events is 19%. 100,000 microcovids + 100,000 microcovids = 190,000 microcovids. The arithmetic we do of adding microcovids by the ordinary rules of arithmetic is a good approximation for relatively small numbers of microcovids, but the actual addition of the risks is sublinear, it does not follow normal arithmetic.
That said, in principle I think you are right that two covid-inhaling events close enough in time will add in a superlinear way for biology reasons. That could be, as you suggest, getting a worse case of covid. It could also be catching covid, when neither event was bad enough on its own to do that. Lets say the threshold to be infected is 100 virus particles (I have no idea the actual number), and each event gives you 75 virus particles. If they happen far enough apart, you don’t get covid, but if they happen one right after the other, you do get covid. Overall, I expect this effect to be small. Unless you are doing super risky things, or working in the covid ward of your local hospital, you probably aren’t encountering two infected people right in a row.
More concerning still is the possibility of simultaneous URTI’s.