Thimerosal is a mercury-containing preservative that has
been used since the 1930s to prevent contamination of vials that contain more
than one dose of vaccine (multi-dose).
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| Multi-dose vial of flu vaccine (CDC/Jim Gathany) |
The tops of vials are disinfected with alcohol before each
use, but alcohol cannot kill all of the microorganisms that might be present,
so bacteria or fungi can be introduced into the vial when the stopper is
punctured with a needle. Since vaccines contain proteins and other nutrients,
bacteria and fungi can multiply inside the vial. Thimerosal kills
microorganisms and prevents potentially fatal vaccine reactions.
Because the stopper is punctured only once, single-dose vials
do not contain thimerosal. Prefilled syringes of flu vaccine and live
attenuated influenza vaccine (LAIV) also do not contain thimerosal.
Other than localized reactions to thimerosal (pain/redness/swelling
at the injection site) and rare allergic reactions, no harmful effects from the
amount of thimerosal in vaccines has ever been demonstrated. However, in
response to public concerns over mercury exposure, the U.S. Public Health Service
and American Academy of Pediatrics issued a joint statement in 1999
recommending the removal of thimerosal from all vaccines routinely administered
to children (CDC,
1999; Finn & Egan, 2008).
In the United States, all vaccines routinely administered to
children do not contain thimerosal or contain only a trace amount of
thimerosal. Influenza vaccine is the single exception to that rule. Influenza
vaccine formulations in multi-dose vials contain thimerosal, but single-dose
vials and prefilled syringes of trivalent inactivated influenza vaccine (TIV;
the “flu shot”) do not contain thimerosal. Live attenuated influenza vaccine (LAIV;
“nasal spray” flu vaccine) does not contain thimerosal.
Neither CDC’s Advisory Committee on Immunization Practices
nor the American College of Obstetricians and Gynecologists express a
preference for thimerosal-free influenza vaccines for pregnant women (ACOG,
2010; CDC,
2010). Nevertheless, thimerosal-free influenza vaccines are available for
adults and children.
Everything you need to know about thimerosal:
Thimerosal in vaccines is a contentious issue. I’ve included
links to information on thimerosal below.
These are my take-home messages:
·
All routine childhood immunizations are
thimerosal-free or contain only a trace amount of thimerosal.
·
Influenza vaccines are available in thimerosal
free formulations.
·
Some states, including Washington, Oregon, and California
have laws restricting the use of thimerosal-containing vaccines.
Thimerosal content of vaccines:
More information on thimerosal:
References:
American College of Obstetricians and Gynecologists. (2010).
Influenza vaccination during pregnancy. Committee Opinion No. 468. Obstetrics
& Gynecology, 116(4), 1006-1007. http://www.acog.org/Resources_And_Publications/Committee_Opinions/Committee_on_Obstetric_Practice/Influenza_Vaccination_During_Pregnancy.aspx.
Centers for Disease Control and Prevention. (1999).
Recommendations regarding the use of vaccines that contain thimerosal as a
preservative. Morbidity and Mortality
Weekly Report, 48(43), 996-998. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4843a4.htm.
Centers for Disease Control and Prevention. (1999).
Thimerosal in vaccines: a joint statement of the American Academy of Pediatrics
and the Public Health Service. Morbidity
and Mortality Weekly Report, 48(26), 563-565. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4826a3.htm.
Centers for Disease Control and Prevention. (2010).
Prevention and control of influenza with vaccines: recommendations of the
Advisory Committee on Immunization Practices. Morbidity and Mortality Weekly
Report, 59(8). http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5908a1.htm.
Finn, T. M. & Egan, W. (2008). Vaccine additives and
manufacturing residuals in United States-licensed vaccines. In S. A. Plotkin,
W. A. Orenstein, & P. A. Offit (Eds.) Vaccines
(5th Ed.). [Electronic version].
The most interesting paragraph in this entry was the following:
ReplyDelete"Other than localized reactions to thimerosal (pain/redness/swelling at the injection site) and rare allergic reactions, no harmful effects from the amount of thimerosal in vaccines has ever been demonstrated. However, in response to public concerns over mercury exposure, the U.S. Public Health Service and American Academy of Pediatrics issued a joint statement in 1999 recommending the removal of thimerosal from all vaccines routinely administered to children (CDC, 1999; Finn & Egan, 2008)."
So despite there being no scientific evidence at all for adverse reactions or any other harm or even a mechanism for possible harm, and solely based on perceived public concern rather than any evidence, we have this huge outrage at thimerosal and, in turn, vaccines in general.
Brilliant logic there from the anti-vaccine crowd.
Thanks Brett,
DeleteYour comment brings up two principles that are relevant to the perception vaccine-associated risk.
The first is "the dose makes the poison." There is a level of exposure below which a potentially toxic substance will have no effect on the body. Mercury is toxic, but no harm from the amount of mercury that used to be in vaccines has ever been demonstrated.
The second is that science cannot prove a negative. Scientific experiments are designed to demonstrate effect. In statistical terms, no effect is the null hypothesis and demonstration of an effect is the alternative hypothesis. Evidence is either sufficient to reject the null hypothesis (demonstrate an effect) or insufficient to reject the null hypothesis. The null hypothesis is never "accepted." This means that nothing can ever be scientifically proven to be "safe" (absence of a harmful effect). What we can say is that the probability that there is a harmful effect is very small.