There have been many such studies using hookworms to investigate whether aspects of out physiology can benefit from parasites, whether our bodies have evolved to expect them to the point that living without is unnatural. BUT, my understanding is that these studies have always used only male or only female worms. The patient is "infected" with a very limited number and they will all eventually die. That is very different than being infested with a colony's worth of worms. And, most importantly, any released eggs will not ever go on to infect other people.

These worms are also easily eradicated from the body if needed. Ivermectin cannot kill covid, but it murders worms very well.