CDC - Seasonal Influenza (Flu) - Questions & Answers - Thimerosal and 2011-2012 Seasonal Flu Vaccines

http://www.cdc.gov/flu/protect/vaccine/thimerosal.htm[04/30/12 04:14:57 PM]

Thimerosal and 2011-2012 Seasonal

Flu Vaccines

Questions & Answers

What is thimerosal?

Thimerosal is a mercury–based

preservative that has been used for

decades in the United States in multi–

dose vials (vials containing more than

one dose) of some vaccines to prevent

the growth of germs, bacteria and fungi,

that can contaminate them.

What are preservatives and

why are they sometimes used

in vaccines?

Preservatives have been used in

vaccines for more than 70 years and are

added to vaccines to prevent the growth

of bacteria or fungi that could possibly

make the vaccine in multi–dose vials

unsafe. This may occur when a syringe

needle enters a vial as a vaccine is being

prepared for administration.

Contamination by germs in a vaccine

could cause serious infections.

Do the 2011-2012 seasonal flu

vaccines contain thimerosal?

The Food and

Drug

Administration (FDA) has approved several formulations of the

seasonal flu vaccine, including multi–dose vials and single–

dose units. (See Table of Approved Influenza Vaccines for the

U.S. 2011–2012 Season.) Since seasonal influenza vaccine is

produced in large quantities for annual immunization

campaigns, some of the vaccine is produced in multi–dose

vials, and contains thimerosal to safeguard against possible

contamination of the vial once it is opened.

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Questions & Answers

What is

thimerosal?

What are

preservatives

and why are

they

sometimes

used in

vaccines?

Do the 2011–

2012 seasonal

flu vaccines

contain

thimerosal?

Is thimerosal

being used in

other

vaccines?

Is thimerosal

in vaccines

safe?

Is thimerosal

in vaccines

linked to

autism?

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CDC - Seasonal Influenza (Flu) - Questions & Answers - Thimerosal and 2011-2012 Seasonal Flu Vaccines

http://www.cdc.gov/flu/protect/vaccine/thimerosal.htm[04/30/12 04:14:57 PM]

The single–dose units are made without thimerosal as a

preservative because they are intended to be opened and used

only once. Additionally, the live–attenuated version of the

vaccine (the nasal spray vaccine), is produced in single–dose

units and does not contain thimerosal.

Is thimerosal being used in other vaccines?

Since 2001, no new vaccine licensed by FDA for use in children

has contained thimerosal as a preservative, and all vaccines

routinely recommended by CDC for children younger than 6

years of age have been thimerosal–free, or contain only trace

amounts of thimerosal, except for multi–dose formulations of

influenza vaccine. The most recent and rigorous scientific

research does not support the argument that thimerosal–

containing vaccines are harmful. However, CDC and FDA

continually evaluate new scientific information about the safety

of vaccines.

Is thimerosal in vaccines safe?

Yes. There is a large body of scientific evidence on the safety of

thimerosal. Data from several studies show the low doses of

thimerosal in vaccines do not cause harm, and are only

associated with minor local injection site reactions like redness

and swelling at the injection site.

Three U.S. health agencies (The Centers for Disease Control

and Prevention (CDC), the Food and Drug Administration

(FDA), and the National Institutes of Health (NIH)) have

reviewed the published research on thimerosal and found it to

be a safe product to use in vaccines. Three independent

organizations [The National Academy of Sciences’ Institute of

Medicine, Advisory Committee on Immunization Practices

(ACIP), and the American Academy of Pediatrics (AAP)]

reviewed the published research and also found thimerosal to

be a safe product to use in vaccines. The medical community

supports the use of thimerosal in influenza vaccines to protect

against potential bacterial contamination of multi–dose vials.

Is thimerosal in vaccines linked to autism?

Numerous studies have found no association between

thimerosal exposure and autism. CDC places a high priority on

vaccine safety, surveillance, and research. CDC is aware that

the presence of the preservative thimerosal in vaccines and

allegations of a relationship to autism have raised public

concerns. These concerns have made decisions surrounding

vaccinations confusing and difficult for some people. Since

2001, no new vaccine licensed by FDA for use in children has

contained thimerosal as a preservative and all vaccines

routinely recommended by CDC for children younger than 6

years of age have been thimerosal–free, or contain only trace

amounts of thimerosal, except for some formulations of

influenza vaccine. Unfortunately, reductions in the numbers of

children identified with autism have not been observed

indicating that the cause of autism is not related to a single

exposure such as thimerosal.

The federal government is committed to ensuring the safety of

vaccines. This is achieved by FDA oversight of rigorous pre–

licensure trials and post–licensure monitoring by CDC and FDA.

This commitment stems from scientific, medical and personal

dedication.

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CDC - Seasonal Influenza (Flu) - Questions & Answers - Thimerosal and 2011-2012 Seasonal Flu Vaccines

http://www.cdc.gov/flu/protect/vaccine/thimerosal.htm[04/30/12 04:14:57 PM]

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Page last reviewed: August 18, 2011

Page last updated: August 18, 2011

Content source: Centers for Disease Control and Prevention,

National Center for Immunization and Respiratory Diseases

(NCIRD)

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