Flu Shots: What’s In the Seasonal Influenza Vaccine?


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FluZone is one of the brand of flu vaccines this year. Photo by: CDC

FluZone is one brand of flu vaccines available this year. Photo by: CDC

The 2012-2013 influenza epidemic continues across the United States. The Centers for Disease Control and Prevention (CDC) reports that for the week ending in January 12, 2013, 48 states have reported widespread flu activity and 29 children (18 years and younger) have died from the flu.

The CDC is recommending that everyone six months and older receive the flu shot. However, some people are skeptical when it comes to what is in the ingredients. Let’s take a look at the Fluzone shot to see what’s in there.

What’s in the Flu Shot?

The flu shot contains three types of dead flu viruses: influenza A (H1N1), influenza A (H3N2), and influenza B, according to the U.S. Food and Drug Administration.

These viruses are selected each year by experts from the FDA, CDC, and the World Health Organization (WHO) who study flu patterns and predict which viruses will be the most ‘popular’ so to speak.

It’s an educated guess at best, but during the first week of January 2013, 91 percent of the influenza viruses that have been tested were the same viruses that are in the vaccine.

Is the Flu Shot Safe? What About Mercury?

Preservatives in the flu shot are needed to prevent contamination, according to the CDC. The preservative that we find in multi-dose flu shots is thimerosal (ethylmercury). Vaccine labs add Thimerosal to multidose vaccines because each time a new needle is inserted into the vial, there is a chance of introducing microbes into the vaccine and contaminating it. The amount of thimerosal in the 0.5mL dose of FluZone is 25mcg.

Mercury in Flu Vaccines: The amount of a chemical a person can have in their bodies without having adverse health affects is called a reference dose. The reference dose for methylmercury is 0.1 µg/kg body weight/day, or .1 microgram per kilogram of body weight per day.

A 40 lb child is about 18 kilograms, which makes the safe dose about 1.8 micrograms – many times less than the dose in a flu shot. Thimerosal, however, isn’t methylmercury, it’s ethylmercury – so what’s the safe dose? The research on safe doses of ethylmercury is extremely sparse, so the dosage is generally based on the more toxic methylmercury.

Due to the controversy over safety, childhood vaccines, other than the flu shot, no longer contain Thimerosal in the United States. If you’re concerned about mercury in your child’s vaccine, you can ask for the thimerosal-free flu shot.

Flu Vaccine: What Else is In There?

The flu shot also contains the following ingredients: sodium phosphate – buffered isotonic sodium chloride solution, formaldehyde, octylphenol ethoxylate, and gelatin, according to the FDA. The influenza virus is grown in chicken eggs and scientists collect the virus and inactivate it by using formaldehyde. They then purify the influenza virus and suspend it in a sugar solution before splitting it with oxtylphenol ethoxylate. After splitting, the scientists purify the virus once more, then suspend it in a salt solution (sodium phosphate – buffered isotonic sodium chloride) and use gelatin to help keep the viruses stable and potent during storage.


The flu shot is given in the arm. Photo by: National Cancer Institute.

Formaldehyde in Vaccines: Vaccine labs dilute the formaldehyde during the making of the vaccine but you will still find residual quantities in the vaccine – ≤50 mcg in the .25mL dose, and and ≤100 mcg in the 0.5mL dose. According to the FDA, the small amount of formaldehyde is considered safe because it also occurs naturally in our bodies in much larger quantities than we get from vaccines. Formaldehyde is also commonly found in household products from cleaners to building materials. The FDA reports that newborns (six to eight pounds) already have 50-70 times the amount of formaldehyde in their bodies than what they would be exposed to with vaccines.

Octylphenol ethoxylate is used to split the influenza virus. Octylphenol ethoxylate is a thick liquid or waxy solid and can be clear to light orange in appearance, according to the Scottish Environmental Protection Agency. It is commonly used in cleaning products, added to paints, textiles, and used in the paper making process. The Scottish Environmental Protection Agency reports that exposure to normal amounts is very unlikely that it would have any adverse health effects on human health.

Gelatin is used as a stabilizer for the vaccines, and as a food product is generally considered safe although those with personal beliefs that prohibit the use of animal or pork products may protest.

Flu Shot Breakdown

While the ingredients in vaccines may sound strange, there are reasons why the labs include them in the vaccines. If you are still unsure about the safety of the flu vaccine, or concerned about the chemicals included, talk with your doctor about your concerns. People who are allergic to eggs should talk to their doctor before getting the flu shot, but most people with an egg allergy can safely receive the vaccine.


Centers for Disease Control and Prevention. Situation Update: Summary of Weekly FluView. (2013). Accessed January 21, 2013.

Centers for Disease Control and Prevention. What You Should Know for the 2012-2013 Influenza Season. (2013). Accessed January 21, 2013.

Centers for Disease Control and Prevention. Vaccine Ingredients. (2012). Accessed January 22, 2013.

DrugLib. Fluzone (Influenza Virus Vaccine) Description and Clinical Pharmacology. Accessed January 22, 2013.

Food and Drug Administration. FluZone. (2012). Accessed January 21, 2013.

Food and Drug Administration. Common Ingredients in U.S. Licensed Vaccines. (2011). Accessed January 22, 2013.

Scottish Environmental Protection Agency. Octylphenol ethoxylates. Accessed January 22, 2013.

United States Environmental Protection Agency. Human Exposure to Mercury. (2012). Accessed January 22, 2013.

Institute of Medicine. Comparative Toxicity of Ethyl and Methyl Mercury. Accessed January 22, 2012.

Barrett, J. Thimerosal and Animal Brains: New Data for Assessing Human Ethylmercury Risk. (2005). Accessed January 22, 2012.

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