system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: During first contacts, why is only the native population at risk for decimation from unseen diseases and not the foreigners?

In relation to the recent saga of the American killed by North Sentinelese tribesmen, I saw this quote in an article: "There are fears 21st century diseases such as the mild common cold could kill off the tribe."

Why is it always the native population that are at risk in these situations and not the outsiders? Couldn't the North Sentinelese have a disease among them that they know to be relatively harmless but could easily kill non-natives?
gpt
Simply said, it is possible but because we live in much denser places and have a global exchange of pathogenes, we are more likely to carry a (deadly) disease than them. Further, we have cuttibg edge med. technologies if it comes hard on hard.