It’s no secret the flu vaccination was designed to help protect you from getting sick with the flu, but can it also cause unwanted side effects? In the United States, flu shots are recommended for everyone 6 months of age and older, as it can cause serious complications for the very young and old. We know that within the influenza vaccine is a form of the flu virus itself, so what are the chances the shot can leave you sicker than before?

Let’s dig deeper. Each flu shot protects against 3 to 4 viruses, and every once in a while, a person will come in contact with a strain that their shot does not protect them from. According to the Centers for Disease Control and Prevention, the flu vaccine is simply a preventive tool to reduce the risk of flu-associated hospitalizations, especially among children and adults. It is also a crucial step to take for people with chronic conditions that are already straining their immune systems.

Reported Reactions:

The vaccine is made from an inactivated virus, which means it’s unable to transmit infection, so people who do get sick after they receive the vaccine were going to get sick regardless. The vaccine takes 1 to 2 weeks to kick in before it’s in full-force protection mode. Because the flu mutates each year, it’s important to get the new shot in order to protect yourself from the strains that are circulating and most likely to cause an outbreak in the current season.

The flu shot is not without its side effects. The CDC reports that people sometimes experience a sore arm at the injection shot. People may also experience a fever, muscle pain, hives, a rash, headache, nausea, and feelings of discomfort or weakness within a few days of the initial shot. In November 2015, out of those surveyed in a study published in the journal Vaccine, 86 to 92 percent reported redness while 50 to 59 percent reported swelling, and 33 to 45 percent reported itching.

There are some extreme reactions reported each flu season and though rare, have been considered life threatening. Up to 2 people out a million vaccinated experience potentially fatal illness, permanent disability, or even death. In extremely rare cases, the flu vaccine can cause Guillain-Barré syndrome, which is a neurological condition that causes weakness and paralysis throughout your entire body. But in the end, you’re more likely to die from getting the flu than experiencing an adverse effect from the flu vaccine.

CORRECTION Oct. 8, 8:20 am ET: Because of a typographical error, this story originally stated that the chance of a potentially fatal reaction to a flu vaccine is 2 percent. It is 2 in a million.