I imagine he might not be the first person who did, the rest are just lost to history due to lack of observable / recorded results.
Earlier generations of people tended to have kind of a general, observation based understanding of that kind of thing where cause and effect was generally observed but people didn’t understand the why of it. People even very early on knew that if you caught a disease once you were less likely to catch it severely again, and they knew that if you quarantined a group of people the disease would eventually “die out”, but they had no real idea as to why in either case.