Is Preservative-Free Flu Vaccine Safer?

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 that are offered in multi-dose vials.

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.

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 them. Thimerosal was one such ingredient that is often blamed is thimerosal. Due to unwarranted public fear, thimerosal has not been used in any vaccine other than the multi-dose flu vaccine since 2001.

In fact, the U.S. Food and Drug Administration (FDA), Centers for Disease Control and Prevention (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.

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:

• Anyone with a severe egg allergy
• Anyone with a history of Guillain-Barre syndrome
• Anyone with an allergy to any of the ingredients in the flu vaccine
• Anyone with a significant fever at the time of vaccination
• Infants under 6 months old

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. Alternately, you can ask your doctor if FluMist is a reasonable option.

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.