Most flu vaccines are “flu shots” given with a needle, usually in the arm, but there also is also a nasal spray flu vaccine. To understand how the flu vaccine works, you need to understand how your immune system works first. Pin On Branding Typical flu symptoms include fever, cough, muscle aches and pains, nasal congestion, headache, sore throat and fatigue. How flu shot works for dummies . Influenza is a respiratory illness commonly known as ‘the flu’. During seasons when flu vaccine viruses are similar to circulating flu viruses, flu vaccine has been shown to reduce the risk of having to go to the doctor with flu by 40 percent to 60 percent. With expert input from rachael lee, md, assistant professor in the uab division of infectious diseases, we explain the differences in flu strains, including how many strains exist and what the flu shot will cover this year. The flu shot is made with an inactivated virus, which means you can’t develop the flu from the seasonal flu vac...