We do think they're very 'frequent': "Astronomers estimate that several interstellar objects of extrasolar origin (like ‘Oumuamua) pass inside the orbit of Ear

We do think they're very 'frequent': "Astronomers estimate that several interstellar objects of extrasolar origin (like ‘Oumuamua) pass inside the orbit of Earth each year, and that 10,000 are passing inside the orbit of Neptune on any given day." https://en.wikipedia.org/wiki/%CA%BBOumuamua#Other_interstellar_objects https://en.wikipedia.org/wiki/%CA%BBOumuamua#Other_interstel...