It's amazing how many people seem to be more scared of the vaccine itself than the potentially deadly disease that it's designed to protect against. In fact, a 2012 survey by CVS Pharmacy found that about 35 percent of Americans actually believe that getting vaccinated can give you the flu [source: Weise and Szabo].
That's enough to make medical experts just shake their heads. Injected flu vaccines use what are called "inactivated" vaccines, which essentially have been killed with chemicals. That process leaves just enough proteins in the outer coating of the virus intact that it tricks your immune system into thinking that the virus is a threat. That causes your body to produce white blood cells that are primed to attack any subsequent viral invader that has the same telltale proteins in its coating as the dreaded flu virus. But that crippled microbe itself is incapable of infecting the body and reproducing itself, which is what would make you sick [source: Weise and Szabo].
The FluMist nasal spray vaccine, which is sometimes given to children, does contain a live weakened virus. But the microbe in that vaccine is "cold-adapted," meaning that it's been changed so that it can cause an infection only at the cooler temperatures found in the nose. [source: Weise and Szabo].
That said, the flu vaccine can sometimes cause side effects. These generally range from redness or swelling at the injection site, to headaches and low-grade fevers [source: NFID]. And some people, as we noted in the previous section, shouldn't get flu shots because of certain medical conditions, at least not without consulting their doctors.