When I feel my throat acting up a bit I gargle with " Betadine Solution Povidone - Iodine 10%".
Dilute it to another 10% for the gargle.
Sore Throat - Betadine (Povidone-iodine) | Betadine
The moment you feel a sore throat coming on, use Betadine® Antiseptic Sore Throat Gargle to treat and relieve sore throat symptoms.
www.betadine.com
The item I link to is a lot less expensive than the prediluted. Just dilute it for gargling.