If your nose is clogged, why can you breathe through your mouth?

If your nose is clogged you can breathe through your mouth because the nasal passages open into the nasal cavity which opens into the back of your mouth at the top of your throat. There are two passages down your throat - your oesophagus and trachea. The oesophagus leads down into your stomach and the trachea leads into your lungs. While you can breathe through your mouth when your nose is blocked, it is important to breathe through your nose instead of your mouth. Your nose contains tiny hairs which act as filters to filter out dust and other contaminants in the air. 

No, when getting the flu vaccine no drugs should be being takin at the time.