Wondering About Thimerosal, Flu Vaccines and Autism? Here's the Scoop on Flu Vaccines From the CDC

Tonight, ABC will be broadcasting the first episode of a fantasy drama entitled Eli Stone. For a show that promises to be pretty silly, it has garnered a tremendous amount of attention - mainly because of a letter sent by the American Academy of Pediatrics (AAP) to ABC asking that the show be pulled. The reason: the case taken by the hero-lawyer involves a plaintiff who claims that her son's autism was caused by thimerosal (a mercury-based preservative) in a flu shot. The lawyer wins a multi-million dollar settlement against the pharmaceutical company named in the suit.

According to the AAP, there is no connection between thimerosal and autism - and presenting such a connection could lead to parents choosing not to vaccinate their children. This, they say, could lead to a public health catastrophe. According to autism advocacy groups such as Generation Rescue, however, the connection is real.

If you've been following the debate, you may well have decided to just skip the flu shots this year. But if you're debating the options, you may want to know whether there are thimerosal-free shots available.

Here's the info, straight from the CDC; from what I can tell, the takeaway message is - run, don't walk, if you're looking for thimerosal-free vaccines in the coming year! It's also important to note that the CDC considers vaccines with "trace amounts" of thimerosal to be "thimerosal free;" I'm assuming (though I don't know for sure) that that applies not only to flu vaccines but also to other preserved vaccines.

For those new to this issue, it's important to know that the MMR vaccine, which is also considered by some to be linked to autism, does not (and never did) contain mercury-based preservatives. The controversy over the MMR relates to the measles virus, and the theory linking the MMR to autism is completely separate from the theory presented in tonight's TV show.

What is thimerosal?

Thimerosal is a very effective preservative that has been used since the 1930s to prevent contamination in some multi-dose vials of vaccines (preservatives are not required for vaccines in single dose vials). Thimerosal contains approximately 49% ethylmercury. There is no convincing evidence of harm caused by the low doses of thimerosal in vaccines, except for minor reactions like redness and swelling at the injection site. However, in July 1999 the Public Health Service (PHS) agencies, the American Academy of Pediatrics (AAP), and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines as a precautionary measure.

Today, all routinely recommended licensed pediatric vaccines that are currently being manufactured for the U.S. market, with the exception of influenza vaccine, contain no thimerosal or only trace amounts. Thimerosal preservative-free influenza vaccines are available, but in limited quantities. The total amount of inactivated influenza vaccine available without thimerosal as a preservative will continue to increase as manufacturing capabilities are expanded.

Does the influenza vaccine contain thimerosal?

Yes, the majority of influenza vaccines distributed in the United States currently contain thimerosal as a preservative. However, some contain only trace amounts of thimerosal and are considered by the Food and Drug Administration (FDA) to be preservative-free. Manufacturers of preservative-free flu vaccine use thimerosal early in the manufacturing process. The thimerosal gets diluted as the vaccine goes through the steps in processing. By the end of the manufacturing process there is not enough thimerosal left in the vaccine to act as a preservative and the vaccine is labeled "preservative-free". Is influenza vaccine that does not contain thimerosal as a preservative available this flu season (2007-08)?

At the current time, sanofi pasteur is projecting that 10 million to 12 million doses of thimerosal-free vaccine in pre-filled syringes or vials will be produced for the 2007-08 influenza season. The majority of this vaccine will be in 0.25 mL syringes (indicated for ages 6-35 months) with the remainder in 0.5 mL vials or syringes (indicated for ages 36 months and older). MedImmune is projecting up to 7 million doses of thimerosal-free nasal vaccine, FluMist, will be produced for the 2007-08 season. In addition, the single dose syringe preparation of CSL Biotherapies’ product, Afluria, is thimerosal-free and can be used in persons 18 years of age and older. Finally, both Novartis and GlaxoSmithKline are producing preservative-free (trace thimerosal) influenza vaccines this season. Novartis’s Fluvirin (single dose syringe preparations) can be used in persons 4 years of age and older and GSK’s Fluarix can be used in adults 18 years of age and older.

Will the supply of thimerosal-free and preservative-free (trace thimerosal) influenza vaccine during the 2007-08 season be adequate for children aged 6-59 months who are recommended for routine influenza vaccination?

For the 2007-08 season, there is one product licensed for 6-23 month old children (the product is thimerosal-free). Given the uptake of influenza vaccine among children < 2 years of age to date and the anticipated increase in vaccine coverage this season, CDC projects that the vaccine supply for this agegroup will be adequate to meet demand.

For children between the ages of 2 and 5 years of age, there are three products available that are thimerosal-free (sanofi’s Fluzone; MedImmune’s FluMist) or preservative-free (trace thimerosal- [Novartis’s Fluvirin]). Specific information about these products and other influenza vaccines can be found in the Table: Influenza Vaccine Manufacturers for the 2007-08 Influenza Season.

Because there are only two products that can be used to vaccinate 3 year-old children, CDC projects that while the national supply of thimerosal-free or preservative-free (trace thimerosal) vaccine may be adequate to meet demand, some providers may not have a sufficient amount of the vaccine type they need to serve all of their 3 year-old patients because the vaccines are not completely interchangeable (e.g., one vaccine can only be used in healthy children).