human
I've heard that the flu shot can cause flu-like symptoms. Is this true?
assistant
Yes, the flu shot can cause flu-like symptoms. The influenza virus is a single stranded RNA virus and it replicates in your body by invading cells and using their machinery to replicate itself. Vaccines are made from killed or weakened versions of the virus so when you get vaccinated you're getting an immune response to the vaccine antigens (which are proteins found on the surface of the virus). This causes some people to experience mild side effects such as soreness at the injection site, fever, fatigue, headaches, muscle aches, and joint pain which are all typical signs of the flu.