There is a filter. But I think it’s mostly there for psychological reasons. First of all the diameter of the snot collection tube, for lack of a better term, increases several fold right after the orifice. That means the velocity of the air drops a lot (precise measurements would be needed to quantify “a lot”, but it’s likely around a 4x-8x drop in velocity) and so any solids settle out onto the sides of the tube.
It might be possible to aspirate aerosol droplets without the filter, but again, you’re aspirating your own baby’s snot in that case which - in case you’ve never had a baby - you aspirate everything from the child anyway. Every bodily fluid they have ends up on every imaginable surface of your self. I’m not worried about germs - even germs “galore” - from their snot.
