Listerine is just drinking alcohol with a few things added which make it harder to drink   Ethanol, which is toxic to bacteria at concentrations of 40%, is present in concentrations of 21.6% in the flavored product and 26.9% in the original gold Listerine Antiseptic.  So Listerine is basically 50 proof booze. Any fairly hard alcohol will do. You could dilute it a bit. Just remember to spit it out! Ive seen a few other studies that looked at lavages for reducing viral load. Some were using salt water and included snorting or spraying the lavage into your nasal passages.  Anyway it appears 1.5% peroxide doesnt do much.