All humans are at least visited by one alien who was turned into a Xenomorph and in turn get converted to be one themselves - the chestbuster doesn't chestbust but takes over the body - only the body, the mind stays conscious. The body will go into a cocoon/doll and emerge as a not-blind Xenomorph.

Since there aren't enough human Xenomorphs, everybody will be captured, put into chains and sent to circus all around the universe. Each of them will eventually break free and one by one, each planet is converted while the human brains watches in horror.