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Updated: Sep 14, 2004
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
contain no thimerosal or only trace amounts.
Updated: Sep 14, 2004
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'.
Updated: Sep 14, 2004
Can I get an influenza vaccine that does not contain thimerosal?
For the 2004-2005 flu season, a limited number of individually packaged doses
of preservative free, reduced thimerosal-content influenza vaccine are available
from Evans Vaccines and Aventis Pasteur. The Evans reduced thimerosal-content
vaccine is approved for use in persons over the age of 3 years. In September
2002, the FDA approved Aventis Pasteur's Fluzone® Preservative-free: Pediatric
Dose, Influenza Virus Vaccine for use in children 6 months of age and older.
Fluzone® is packaged in 0.25 ml dose syringes for persons under 3 years
of age, and in 0.50 ml dose syringes for persons 3 years and older (including
pregnant women).
Updated: Sep 14, 2004
Is it safe for children to receive an influenza vaccine that contains thimerosal?
Yes. There is no convincing evidence of harm caused by the small doses
of thimerosal in vaccines, except for minor effects like swelling and redness
at the injection site due to sensitivity to thimerosal. Most importantly, since
1999, newly formulated thimerosal preservative-free childhood vaccines (Hepatitis
B, Hib, and DTaP) have been licensed. With the newly formulated childhood vaccines,
the maximum total exposure during the first six months of life will now be less
than three micrograms of mercury. Based on guidelines established by the FDA,
the Environmental Protection Agency (EPA) and the Agency for Toxic Substances
and Disease Registry (ATSDR), no child will receive excessive mercury from childhood
vaccines regardless of whether or not their flu shot contains thimerosal as a
preservative.
Recent research suggests that healthy children under the
age of 2 are more likely than older children and as likely
as people over the age of 65 to be hospitalized with flu
complications. Therefore, vaccination with reduced or standard
thimerosal-content flu vaccine is encouraged when feasible
in children, including those that are 6-23 months of age.
Updated: Sep 14, 2004
Is it safe for pregnant
women to receive an influenza vaccine that contains thimerosal?
Yes. A study of influenza vaccination
examining over 2,000 pregnant women demonstrated
no adverse fetal effects associated with influenza
vaccine. Case reports and limited studies indicate
that pregnancy can increase the risk for serious
medical complications of influenza. One study
found that out of every 10,000 women in their
third trimester of pregnancy during an average
flu season, 25 will be hospitalized for flu
related complications.
Additionally, influenza-associated excess deaths among
pregnant women have been documented during influenza
pandemics. Because pregnant women are at increased
risk for influenza-related complications and because
a substantial safety margin has been incorporated
into the health guidance values for organic mercury
exposure, the benefits of influenza vaccine with reduced
or standard thimerosal content outweighs the theoretical
risk, if any, of thimerosal.
References
Ball LK, Ball R, Pratt RD. An assessment of thimerosal use in childhood vaccines.
Pediatrics 2001;107(5):1147-54.
Centers for Disease Control and Prevention. Prevention and control of influenza;
recommendations of the Advisory Committee on Immunization Practices (ACIP).
MMWR 2002; 51(RR03):1-31.
Centers for Disease Control and Prevention. Recommendations regarding the
use of vaccines that contain thimerosal as a preservative. MMWR 1999;48(43):996-8.
Heinonen OP, Shapiro S, Monson RR, Hartz SC, Rosenberg L, Slone D. Immunization
during pregnancy against poliomyelitis and influenza in relation to childhood
malignancy. Int J Epidemiol 1973;2:229–35.
Izurieta HS, Thompson WW, Kramarz P, et al. Influenza and the rates of hospitalization
for respiratory disease among infants and young children. New Engl J Med 2000;342:232–9.
Kirshon B, Faro S, Zurawin RK, Samo TC, Carpenter RJ. Favorable outcome after
treatment with amantadine and ribavirin in a pregnancy complicated by influenza
pneumonia: a case report. J Reprod Med 1988;33:399–401.
Neuzil KM, Wright PF, Mitchel EF, Griffin MR. Burden of influenza illness
in children with asthma and other chronic medical conditions. J Pediatr 2000;137:856–64.
Neuzil KM, Reed GW, Mitchel EF, Simonsen L, Griffin MR. Impact of influenza
on acute cardiopulmonary hospitalizations in pregnant women. Am J of Epidemiol
1998;148(11):1094-102.
Shahab SZ, Glezen WP. Influenza virus. In: Gonik B, ed. Viral diseases in
pregnancy. New York, NY: Springer-Verlag, 1994:215–23.
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