David Banks/AP
Registered Nurse Judy Walker readies a dose of the swine flu vaccine nasal mist at Children's
Memorial Hospital in Chicago, Monday, Oct. 5, 2009.

A New Question Emerges About Thimerosal: Is It Safe for Adults?

October 06, 2009 02:00 PM
by findingDulcinea Staff
With many adults expected to receive the swine flu vaccine/H1N1 influenza vaccine this year, those with a history of allergies to thimerosal may wonder if it’s safe for them.

Thimerosal Allergies and the H1N1 Vaccine

The swine flu vaccine/H1N1 influenza vaccine is expected to result in record numbers of adults getting vaccines this year. Most deliveries of the vaccine will come in multi-dose vials preserved with thimerosal. Yet the patient instructions and package inserts warn against use of the vaccine in patients with known allergies to thimerosal. Given that many adults have experienced allergic reactions to thimerosal in contact lens solutions, eye creams or other cosmetics, patients and health care professionals may question whether the H1N1 vaccine is safe for adults with such histories.

What is thimerosal?

According to the Public Health Agency of Canada, thimerosal is an organic compound that contains mercury. It has been used since the 1930s as a preservative in vaccines and other pharmaceutical products, including cosmetics and contact lens solutions. Thimerosal “prevents bacterial and fungal contamination of these products,” and is added to vaccines as a preservative to prevent contamination, “particularly in multi-dose vials.”

Is the mercury in thimerosal dangerous?

Thimerosal contains ethyl mercury, which is chemically different from methyl mercury,” the National Institute of Allergy and Infectious Diseases explains. Methyl mercury occurs naturally in the environment. People are most commonly exposed to it by eating contaminated fish. At high levels, methyl mercury is toxic and can cause cerebral palsy, seizures in children exposed to it before birth and mental retardation, NIAID reports. 

The FDA cites a study supported by NIAID in 2002 that looked at infants that received vaccines containing thimerosal. According to the FDA, “mercury was cleared from the blood in infants exposed to thimerosal faster than would be predicted for methyl mercury … Thimerosal appears to be removed from the blood and body more rapidly than methyl mercury.”

Does thimerosal in vaccines cause autism?

Some child advocates have long claimed that thimerosal does cause autism. In 2008, U.S. government health officials admitted that a series of vaccinations given to Hannah Poling exacerbated an underlying condition that led to her developing autism.

But the Centers for Disease Control and Prevention’s view is that “there is no conclusive evidence that any vaccine or vaccine additive increases the risk of developing autism or any other behavior disorder.” The CDC cites a 2004 report from the Institute of Medicine that found no association between vaccines that contain thimerosal and autism.

Where does the government stand on thimerosal in vaccines?

Although the CDC asserts there is no “scientific evidence of harm caused by the minute doses of thimerosal in vaccines,” in July 1999 the American Academy of Pediatrics, the Public Health Service and vaccine manufacturers all agreed to reduce or eliminate thimerosal in vaccines as a “precautionary measure.” Except for some flu vaccines, none of the vaccines administered to preschool children in the United States contain thimerosal.

Can someone be allergic to thimerosal?

Yes. According to the North American Contact Dermatitis Group (NACDG), “Thimerosal is the fifth most common allergen,” the journal Dermatitis reported in 2005.

Thimerosal was commonly used as a preservative in contact lens solutions in the 1980s and 1990s. A substantial number of patients developed a delayed allergic reaction to it. Although some reactions were severe, most were similar to conjunctivitis, with red, burning, itchy eyes.

The New Zealand Dermatological Society Incorporated (NZDSI) explains that “allergic contact dermatitis (itchy red patches) may occur in sensitive individuals” that come in contact with thiomersal (an alternative name for thimerosal). The preservative is commonly added to ear, eye and nose drops; eye makeup; antiseptic sprays; and soap-free cleansers. When products containing thimerosal are injected, such as vaccines, redness and swelling may occur at the injection site. Reactions to thimerosal are generally mild and disappear after several days, according to NZDSI.

If I have had a contact allergic reaction to thimerosal, will I have a problem with a thimerosal-containing vaccine?

The package inserts—and patient instructions—for many vaccines state they should not be given to anyone with an “allergy to thimerosal.” Until recently, there has been little information available as to whether this precluded vaccination of people that had experienced mild allergic reactions to thimerosal as a result of skin contact or use in the eyes.

In 1990, the Southern Medical Journal was one of the first publications to address this issue with regard to a hepatitis B vaccine. The journal noted that “Strict interpretation of the package insert … would preclude its administration to anyone with a history of ocular sensitivity to thimerosal.” But it also noted that reports of severe adverse reactions to vaccines containing thimerosal were sparse, and that nine hospital employees had reported ocular sensitivity to thimerosal but experienced no problems with a vaccine. “If others administering the vaccine would ask the proper questions, sufficient numbers could be generated and reported that would either support the contraindication, or lead to a change in its present wording,” the journal concluded.

Yet nearly 20 years later, what was then the present wording contraindicating use in those with allergies to thimerosal remains on many vaccine package inserts. Still, according to the CDC, “Research suggests that most people who have a contact or skin allergy to thimerosal will not have the reaction when thimerosal is injected under the skin….prior history of a minor reaction to thimerosal in a vaccine is not considered a contraindication to further vaccination with thimerosal-containing vaccines.” Conversely, a serious “anaphylactic (allergic) reaction to any vaccine is a contraindication to further vaccination with the vaccine."

In 2005, the medical journal Dermatitis published results of a study in which individuals with known sensitivity to thimerosal were repeatedly injected with it. Only 9 percent of these patients experienced mild local reactions, while 91 percent experienced no reactions at all.

Will the swine flu vaccine/H1N1 influenza vaccine contain thimerosal?

The majority of available doses of the 2009 H1N1 influenza vaccine will be multi-dose vials that contain thimerosal. Single-dose units, which may be difficult to find, will not contain thimerosal as a preservative. Additionally, the “live-attenuated” doses (FluMist®) of the vaccine that are inhaled through the nose will be offered in single-dose units and will not contain thimerosal.

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