Oof, yeah, plague is a nasty one to start off with. Generally the very first “mission” I do after setting up survival essentials is kill and butcher a couple of big animals, then try to sell the meat and leather for penoxycycline at the nearest friendly base. If I can get enough, everyone gets, otherwise it’s just my doctors’ drug policy until I’ve got a steady supply.
You’re still right, though - talking about closest planet on average isn’t very useful, because it’s always going to be the closest planet to the sun. Asking “what planet can get closest to some [Planet]” is more interesting and enlightening.