Is Preservative-Free Flu Vaccine Safer?

Unwarranted autism fear leads to new formulation

In This Article

The preservative-free flu vaccine is a type of flu vaccine that does not contain the preservative thimerosal. Preservative-free flu vaccines come in a single-dose vial, unlike many that are offered in multi-dose vials.

According to the Centers for Disease Control and Prevention, approximately 85% of projected vaccine supply produced for the 2019-2020 flu season will be thimerosal-free (i.e., preservative-free). For this particular season, only multidose vial presentations of influenza vaccines contain thimerosal.

Other than the lack of thimerosal, the formulation contains the same four strains of killed influenza virus as other injectable quadrivalent flu vaccines. Preservative-free flu vaccines are also delivered at the same time and the same dose as the traditional flu vaccines.

According to the CDC, you should get your flu shot before the end of October. Children under nine receiving the vaccine the first time would need a second shot four weeks after the first.

Side Effects of the Preservative-Free Flu Vaccine
Verywell / Cindy Chung

Thimerasol Safety

Thimerosal is a mercury-based preservative that prevents the growth of bacteria, fungus, or other microorganisms that might contaminate the flu vaccine. It is used in multi-dose vials of the flu vaccine for delivery to multiple people.

Back in 1998, a doctor in Great Britain published a small study claiming that the measles, mumps, and rubella (MMR) caused children to develop autism. The study was incredibly flawed both in design and controls. Subsequent research failed to show any link between the MMR vaccine and autism.

However, the study set off a firestorm of misperceptions and falsehood that led many parents to abandon vaccines altogether, as well as any ingredient contained in them. Thimerosal was one such ingredient that was often blamed. Due to unwarranted public fear, thimerosal has not been used in any vaccine other than the multi-dose flu vaccine since 2001.

To date, there has been no evidence that thimerosal can or has ever caused autism in children exposed to the vaccine preservative.

In fact, the U.S. Food and Drug Administration (FDA), CDC, National Institutes of Health (NIH), American Academy of Pediatrics (AAP), Advisory Committee on Immunization Practices (ACIP), and National Academy of Sciences' Institute of Medicine have all declared that the use of thimerosal in vaccines is safe and effective.

Side Effects

Like all injected flu vaccines, side effects of the preservative-free flu vaccine include:

  • Pain and swelling at the injection site
  • Low-grade fever
  • Fatigue

Side effects are typically mild and resolve within a day or two. However, you develop severe pain, increased swelling, nausea, vomiting, rash, rapid heart rate, or difficulty breathing, call 911 or go to your nearest emergency room.


Those who should not get the preservative-free flu vaccine include:


If you would prefer to avoid thimerosal, ask your health provider if they have a preservative-free flu vaccine available. Most immunization clinics and pharmacies will only have one or two types on-hand (typically the traditional multi-dose vial and the FluMist nasal spray) and would have to place a special order.

Because it takes two weeks for the body to produce defensive antibodies after the shot, you would need to place your order early in the season to avoid infection. With the changes made for the 2019-2020 season, however, it shouldn't be too difficult to obtain the thimerosal-free vaccine. Alternatively, you can ask your doctor if FluMist is a reasonable option.

While the FluMist vaccine is thimerosal-free, it contains a live weakened virus and cannot be used in people with compromised immune systems, children under two, people with a severe egg allergy, or the elderly.

A Word From Verywell

Although there has been no evidence that thimerosal causes harm when used in vaccines, there are other options today that do not contain this ingredient.

In the end, remember that preservative-free vaccines come in a single-use vial. Any multi-use vial will invariably contain a preservative. You should ultimately talk to your provider to determine the best option for you.

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Article Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Influenza (flu). Vaccine supply for the2019-2020 season. September 24, 2019.

  2. Centers for Disease Control and Prevention. Influenza (flu). What you need to know for 2019-20. October 8, 2019.

  3. Centers for Disease Control and Prevention. Understanding thimerosal, mercury, and vaccine safety. February 2013. 

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