If you have a fever, you should postpone getting your flu shot until you are fever free; although, you can get the vaccine if you have a respiratory illness without a fever, or if you have another mild illness. The nasal-spray flu vaccine can be given to people with minor illnesses, such as: diarrhea a mild upper respiratory tract infection, with or without a fever. If you have nasal congestion, you should consider waiting to get the nasal-spray flu vaccine. Nasal congestion may limit the vaccine’s ability to reach the nasal lining.