Hmm. I don't know if anyone catches COVID from COVID-infected people's unfinished beverages being in the fridge, but if you can't do that and don't want to throw it out, hmm. If it's the acidity that hurt your throat, maybe try neutralizing it by adding some baking soda? This will make the lemonade salty, so not do this if you're restricting your sodium intake. If you do, add the baking soda carefully to avoid it fizzing out of control and making a mess.