Can I re-catch a cold I have given someone else?



Posted by Ed 8 mths ago
Good question! In general, you're pretty unlikely to re-catch a cold you've passed on recently. Viruses can mutate fast, but the immune system covers a broad enough spectrum that they almost never can mutate that far, that fast.

There are a couple of caveats, though. First, we're talking here about an immediate re-infection -- you're infected today, you infect your child in three days, you clear the infection next week, can he reinfect you three days after that? Under those conditions, the virus hasn't had the chance to mutate very far, plus (critically) your immune response is at its absolute peak during the period of potential re-exposure.

Many of the viruses that cause colds are poorly immunogenic, which means that immunity to them may not last all that long -- 6 months at the lower end, a year or three might be fairly typical. And these viruses are almost all acute viruses, meaning they get eliminated a week or two after infection. So in our scenario, your child is

shedding virus while you still have good immunity, and your child eliminates the virus long before your immunity wanes.

But if you add a few more links to the chain, and the virus cycles through all the kids in the day care, back to their parents, and so on, and then you are exposed to that virus again in a year via a parent's lawyer's child's teacher's wife's mechanic, then yeah, maybe you could be re-infected. Not only is your immunity lower than it was, but the virus has had many more replication cycles to accumulate mutations.

There's another scenario that's a potential concern, and that's when an immunocompromised person is in the infection chain. Viruses are much more prone to accumulating mutations in these conditions. It's kind of like bacteria exposed to low-level antibiotics - the virus is exposed to some parts of the immune system, so it's under selective pressure, but there isn't enough immunity to completely eliminate it, so the virus has a chance to accumulate these anti-immune mutations and pass them on.

There are many, many other potential ramifications and variations, but that covers the most common scenarios, I think.

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