Flu Shots 101: What's in a Flu Shot and Will it Give Me the Flu?

By Haley Bass | 10/13/2017

There’s no question that flu season is coming – every year, starting in the fall, there are notices everywhere about getting vaccinated and washing your hands regularly. But year after year, people still have the same questions about the flu vaccine.

We want to answer all your flu questions so you feel more confident heading into flu season. In part one of our Flu Shots 101 guide, we covered who needs a flu shot and when you should get one. In part two, we’re focusing on what’s in a flu shot, whether the shot is effective, and what side-effects you might experience - including whether the flu shot can give you the flu.

What ingredients are in the flu vaccine?

Most people who ask about flu shot ingredients are typically think it’s a live virus, includes mercury, or could cause an allergic reaction.

Flu vaccines contain either an inactivated virus--meaning it’s not infectious--or a particle that tricks your immune system into thinking it’s a flu virus. So, no live virus. Additionally, flu shots have small amounts of other ingredients, like:

  • Preservatives that prevent contamination
  • Elements that stimulate a stronger immune response
  • Stabilizers that keep the vaccine effective during storage

One of the common preservatives used, thimerosal, is an ethyl mercury-based compound that helps prevent contamination in multi-dose vials of the vaccine. The Centers for Disease Control and Prevention (CDC) states that thimerosal is safe, and there are no links between its use in vaccines and autism. So, while some vaccines contain a tiny bit of mercury in, it is safe.

There might also be tiny amounts of materials that were used during manufacturing and removed, including:

  • Cell culture materials used to grow the vaccine antigens
  • Inactivating ingredients used to kill viruses
  • Antibiotics that prevent bacteria contamination

Egg protein is the most common culture used to grown antigens, which causes people with egg allergies to fear a reaction from the vaccine. However, any trace amount of egg is typically removed before injection, and an allergic reaction is rare.

Is the flu shot effective?

Regardless of how well the vaccine matches the virus strand year-to-year, the flu vaccine is still your best chance to prevent getting and spreading the flu. Recent studies by the CDC have found that the flu shot reduces the overall population’s risk of getting the flu by 50-60% when the vaccine matches most circulating flu viruses.

There are two main factors involved in whether a flu shot will be effective for an individual:

  1. The age and health of the person being vaccinated
  2.  How well the flu vaccine matches the flu viruses spreading in that person’s community

 Will the flu shot give you the flu?

The flu shot can come with some negative side effects, but that’s no different from any other medical product interacting with your body. Most side effects are mild and will go away on their own in a few days.

Flu shot side effects commonly include:

  • Soreness or redness from the shot
  • Headache
  • Fever
  • Nausea
  • Muscle aches

There’s also a rare chance of an allergic reaction, which may result in difficulty breathing, hives, or swelling around the eyes or lips. If you’re having an allergic reaction, the signs will appear soon after the vaccine is given. In an emergency, call 911 or go to the nearest hospital. Otherwise, call your doctor.

One thing you can be sure of - the flu shot does not cause the flu. Flu shots are made with inactivated viruses, so there’s no chance of the vaccine infecting you. If you do experience flu symptoms after your flu shot, it could be from many other reasons. It’s possible to get infected before your shot and not show signs until afterwards, or to get infected within the 1-2 week window before immunity develops. You can also be exposed to a different virus strand than the ones your shot was designed to protect against.

With more than 300 locations across the country, there’s likely a Concentra center near you, and we offer flu shots at every one of them! No appointment required. Find your nearest Concentra center and get the protection you need against the flu.

Resource: The Centers for Disease Control and Protection