Can you get the flu from a flu shot? Does the flu shot even work? We got the answers to your most pressing flu season questions.

By Stacey Leasca
Updated October 01, 2018

As the weather starts to get colder, there's usually one leading ailment on people's minds: the flu. And according to the FDA, the 2018-2019 flu season officially started the last week of September.

Each year, an estimated 200,000 Americans are hospitalized with the flu. Patients come in with aches, pains, fevers, and more, which can last for days or even weeks. In total, between five to twenty percent of Americans will fall victim to the virus this year.

There are, however, ways to prevent the flu from ever taking hold, including getting the flu shot, which the CDC recommends people ages six months and over receive (including breastfeeding women), and especially the elderly, pregnant women, and those with weakened immune systems due to various illnesses–including, in some cases, being sick with a severe enough cold.

But, many people forgo getting a flu shot out of fears that it will make them sick with the flu itself. Here’s everything you need to know about the flu shot and its potential side effects.

What does the flu shot do?

The flu shot, the Centers for Disease Control and Prevention (CDC) explained, “cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with the viruses that are in the vaccine.”

Each year, the CDC tweaks the flu vaccine to better protect the population from the new strains of flu.

Is the virus live in the flu shot?

No, the virus is not alive in the flu shot. However, the CDC notes, “Unlike the flu shot, the nasal spray flu vaccine (also known as the 'live attenuated influenza vaccine' or 'LAIV') does contain live influenza viruses, but the viruses are attenuated (weakened), so that they will not cause flu illness.”

The spray is typically used for children, but the American Academy of Pediatrics (AAP) advised families that the shot is a better option than the spray for the 2018-2019 flu season.

Can you get the flu from the flu shot?

The short answer is no, you cannot get the flu from the flu shot. However, it can take up to two weeks for the vaccine to take effect, so you could still catch the flu during this period.

What are the potential side effects from the flu shot?

According to the CDC, potential flu vaccine side effects can include soreness, redness, or swelling where the shot was given, a low-grade fever, and aches. All of these side effects from the flu shot should be mild and short-lasting.

Does the flu shot work?

Unfortunately, there is no way of predicting the 2018-2019 flu shot's effectiveness completely. FDA Commissioner Scott Gottlieb, M.D., explained in a statement that, based on flu patterns already emerging, this year's shot should be effective at beating the present strains.

However, "effective" is a relative term. Based on the CDC's data, this year's shot is 36 percent effective overall. That means it should reduce a person's risk of catching the flu by one-third. And it may get worse. As VOX notes, the vaccine’s effectiveness against H3N2, the most commonly-circulating strain, is only at about 25 percent. Still, 25 percent is better than zero protection, right?

For more on this year's preventative measure, here's when the best time to get a flu shot is and what signs of the flu to look out for.