Let’s just get the big one out of the way first. This myth has been around for ages. Flu shots are made with dead viruses or without any viruses at all. So you’ can’t catch the flu from a flu shot because the inactivated virus in the shot can’t transmit the disease. Because it takes a few weeks for the vaccine to start protecting your body, people who get sick in those few weeks think the shot caused the illness. It is true, however, that the flu shot may cause flu-like – but mild – symptoms such as feeling tired and muscle ache.