When you are sick (you have a sore throat or chest congestion), it is a good idea to use a new toothbrush in the three stages of your illness, at the start, middle and the end. Germs can form on your toothbrush bristles and make you sick. In my family, we use electric toothbrushes and the heads can get expensive so at the first sign of illness, I give my kids disposable toothbrushes like these.
We change our toothbrush after we feel better when we are sick all the time because I don't want the virus and germ still in the toothbrush.