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Immunization Home > Vaccine Safety > Thimerosal Q and A Thimerosal Q and A

AMERICAN ACADEMY OF PEDIATRICS

Thimerosal in Vaccines - an Interim Report to Clinicians

INTRODUCTION

On July 8,1999, the American Academy of Pediatrics (AAP) issued with the Public Health Service a joint statement alerting clinicians and the public of concern about thimerosal, a mercury-containing preservative used in some vaccines. That statement was disseminated widely, including on the AAP e-mail list and is posted on the Members Only Channel on the AAP Web site at http://www.aao.org/moc. The AAP Board of Directors recognizes that in light of these concerns, clinicians need guidelines today on their infant immunization practices.

What follows is information prepared by our technical committees as sections introduced by the following headings: Thimerosal, Mercury Exposure and Toxicity, Federal Guidelines and Risk of Withholding Vaccines. The AAP Board of Directors then offers specific interim guidelines based on its understanding of the information, which is currently available. This material should allow clinicians to inform parents about thimerosal. It takes advantage of the flexibility of the 1999 Recommended Immunization Schedule with modest modifications, which provide an expansion of the margin of safety for small infants. It is important not to compromise the remarkable protection immunization now offers during that particularly vulnerable time of life.

THIMEROSAL

Thimerosal has been used as an additive to biologics and vaccines since the 1930’s because it is very effective in killing bacteria used in several vaccines and in preventing bacterial contamination, particularly in opened multi-dose containers. Some but not all of the vaccines recommended routinely for children in the United States contain Thimerosal[1 5]. Thimerosal contains 49.6% mercury by weight and is metabolized to ethyl mercury and thiosalicylate. Data are limited regarding potential differences in toxicity between ethyl mercury and methyl mercury. Both forms of organic mercury are associated with neurotoxicity in high doses and definitive data regarding the doses at which developmental effects occur in infants are not available. When vaccines containing thimerosal have been administered in the recommended doses, hypersensitivity has been noted, but no other harmful effects have been reported[16]. Massive overdoses from inappropriate use of thimerosal containing products have resulted in toxicity[17-2 1]. As part of an ongoing review of biologic products in response to the FDA Modernization Act of 1997, the FDA has determined that infants who receive thimerosal-containing vaccines at several visits may be exposed to more mercury than recommended by Federal guidelines for total mercury exposure.

The thimerosal content of vaccines commonly used in children is shown in Table 1(attached). No polio (IPV or OPV), measles, mumps, rubella, varicella, rotavirus or Lyme disease vaccines contain thimerosal[22J. All whole cell DTP preparations contain thimerosal; one acellular product does not. There are several Haemophilus influenzae (Hib) products available that do not contain thimerosal.

MERCURY EXPOSURE AND TOXICITY

Mercury occurs in three forms: the metallic element, inorganic salts, and organic compounds (e.g., methyl mercury, ethyl mercury, and phenyl mercury). The toxicity of mercury is complex and dependent upon form of mercury, route of entry, dose and age at exposure. Mercury is present in the environment in inorganic and organic forms and everyone is exposed to small amounts [1 ,2] The primary environmental exposure to organic mercury is from consumption of predator fish.

As an example of the mercury content of food commonly eaten by older children and adults, an FDA study has indicated that a 6 ounce can of tuna contains an average of 17 (range 1.7-1 27) micrograms of mercury [3]. In some areas of the United States, freshwater fish (eg, walleye, pike, muskie, and bass) may contain elevated concentrations of mercury as well.

Local fish advisories and bans provide information to people about the safety of eating fish. EPA points of contact for such local advisories include: EPA National Center for Environmental Publications and Information (513)489-8190, EPA Office of Water (202)260-1305/fax (202)260-9830, EPA Web site address http://www.epa.gov/OST/fish/.

The major toxicity of organic mercury compounds is expressed in the central nervous system, though the kidneys and the immune system may also be affected [1,2,4]. Organic mercury readily crosses the placenta and blood-brain barrier. When fish taken from waters heavily contaminated with methyl mercury have been ingested during pregnancy severe developmental and neurologic impairment has occurred in children exposed in utero[1 ,2]. Other in utero toxic exposures have occurred when methyl mercury contaminated seed grain was consumed by women [5,6,7]. Organic mercury compounds are readily absorbed by ingestion, inhalation and through the skin. Methyl mercury is distributed to all tissues but concentrates in blood and brain. Ninety percent of methyl mercury is excreted through bile in feces. The average half-life for methyl mercury in blood is 40-50 days (range 20-70 days) for adults and breastfeeding infants [1,7]. Although methyl mercury can be measured in blood or hair specimens. collection of specimens requires special mercury-free collection materials and rigorous control of contamination. Such testing is usually carried out in a research setting.

FEDERAL GUIDELINES FOR LIMITING MERCURY EXPOSURE

In recent years several agencies have been working toward reducing mercury exposure. Guidelines have been established by the Environmental Protection Agency (EPA)[8], the Food and Drug Administration (FDA)[9], and the Agency for Toxic Substances and Disease Registry (ATSDR)[1 0] in an effort to minimize preventable exposures to mercury from food and other environmental sources. Based on the assumption that exposures will continue for long periods of time, maximum recommended allowable daily exposures range from 0.1 micrograms of mercury per kg per day for the EPA[14], to 0.3 micrograms per kg per day for the ATSDR, and to 0.4 micrograms per kg per day for the FDA[8]. The small variability in guidelines from different organizations reflects subtle differences in the populations studied, methods of calculation, the uncertainty inherent in extrapolations, and use of different safety factors.

The primary purpose of the guidelines is to prevent exposure of women of childbearing age to amounts of mercury that might be toxic to the rapidly developing brain of the fetus, which is much more susceptible to toxicity than the adult brain[1]. The specific window of highest susceptibility is not known, but exposure after birth should be associated with less toxicity than in utero exposure. The Federal guidelines for mercury exposure are based upon extrapolations from blood and/or hair concentrations of mercury in pregnant women following inadvertent exposures to high concentrations of methyl mercury from consumption of contaminated grain or fish. The mercury concentrations in blood or hair from exposed women were used to estimate maximum daily oral intakes of methyl mercury during pregnancy that were not associated with measurable adverse outcomes in their children. In earlier studies, blood levels of 100-200 micrograms of mercury per liter in pregnant women were not associated with detectable abnormalities in the children exposed in utero [5,6,7]. Some recent data suggest that exposure in utero to mercury at levels previously thought to be safe may have subtle adverse effects on the developing brain [1 1]. Additional studies are ongoing as data are limited with regard to the effects of low dose or intermittent exposures [12,13]. The Federal Guidelines were not designed for intermittent or bolus exposures.

RISKS OF WITHHOLDING VACCINES

Children who do not receive recommended immunizations are at increased risks of acquiring serious diseases [23]. When immunization acceptance has declined, epidemics of vaccine preventable diseases have occurred as evidenced by the measles outbreaks in this country in 1989-1991, resurgence of pertussis in Japan, Sweden and the United Kingdom in the late 1970’s, and the recent diphtheria epidemic in the former Soviet Union[23,24]. Children who acquire diphtheria have a 3%-23% chance of dying; 25% of children with pertussis are hospitalized, 22% develop pneumonia, 3% have encephalopathy and often suffer permanent sequelae or death. Hepatitis B kills several thousand Americans every year from liver cancer and cirrhosis of the liver [25]. Hib vaccines have resulted in the near elimination of meningitis, pneumonia and sepsis from this organism. Approximately 5% of children with Hib meningitis die and 50% of the survivors have neurologic sequelae including deafness, impaired vision, and mental retardation [26]. Although these diseases have been reduced to record low numbers, the organisms that cause these diseases are still present and unvaccinated children will be at risk. These serious diseases can be prevented through immunization. If thimerosal-free vaccines are not available, physicians and parents must balance the known risks of serious complications from these diseases against the unknown but much smaller risks associated with thimerosal in some vaccines. In high-risk situations such as infants born to hepatitis B surface antigen (HBsAg) positive mothers, the known risks of serious consequences from the preventable infections far outweigh the risks of adverse consequences from vaccines, even if thimerosal-free products are not available.

RECOMMENDATIONS

The AAP urges government agencies to work rapidly toward reducing children’s exposure to mercury from all sources. Because any potential risk is of concern, the AAP and the Public Health Service agree that the use of thimerosal-containing vaccines should be reduced or eliminated. The AAP believes that physicians should minimize children’s exposure to thimerosal, but they should not compromise the health of children by withholding routinely recommended immunizations. This should be possible given the flexibility in the current immunization schedule (eg, see Recommendations number 2 and 3 below).

The following Recommendations are made to optimize vaccine administration and minimize exposure to thimerosal. If there are limited supplies of thimerosal free products available, priority should be given to use in premature infants.

  1. All children should be immunized to protect them against the diseases listed in the 1999 Recommended Childhood Immunization Schedule.
     
  2. Because any potential risk is of concern, the AAP, and the Public Health Service agree that the use of thimerosal-containing vaccines should be reduced or eliminated. The benefits and risks of vaccines containing thimerosal should be discussed with parents. The use of products containing thimerosal is preferable to withholding vaccinations, which protect against diseases that represent immediate threats to young infants (eg, pertussis and Haemophilus influenzae). For hepatitis B vaccine, adjustments in timing within the ranges proposed in the immunization schedule provide additional opportunities to minimize exposure of small infants to thimerosal.
     
  3. The AAP recommendations for prevention of hepatitis B infection:
  • In infants born to HBsAg positive women* and women not tested for HBsAg during pregnancy remain unchanged from the 1999 Recommended Childhood Immunization Schedule.
     
  • At this time the only thimerosal-free hepatitis B vaccine available (COMVAX) also contains Hib vaccine (PRP-OMP). This product is not approved for use before 6 weeks of age because of decreased response to the Hib component. For that reason, where available, this thimerosal-free vaccine may be given to infants born to HBsAg negative women beginning at the two months visit. If thimerosal free vaccine is not available, hepatitis B virus vaccination should be initiated at 6 months of age. Based on the current immunization schedule, for most infants, either of these approaches should allow completion of the necessary three doses of vaccine by 18 months of age. Until thimerosal free vaccine is available, immunization for the small, prematurely born infant should be deferred until the infant reaches a size and developmental level which corresponds to the term infant (as noted above).
     
  • A hepatitis B vaccine, which does not contain thimerosal, is expected to be made available in the near future. When sufficient supplies of this vaccine ate available, it will be appropriate to resume the previous recommendation that immunization may begin in the newborn period.
  1. Manufacturers and the FDA are urged to work toward rapid reduction or elimination of mercury-containing preservatives from immunizations.
     
  2. Infants and children who have received thimerosal-containing vaccines do not need to have blood, urine or hair tested for mercury since the concentrations of mercury would be quite low and would not require treatment.
     
  3. Pediatricians should urge pregnant women, nursing mothers, and young children to follow fish advisories from state health, environmental and conservation officials and should counsel parents about reducing exposures to other sources of mercury. The Academy is developing additional information on this subject.
      
  4. The benefits and risks of vaccines containing thimerosal should be discussed with parents (as with all vaccines). The larger risks of not vaccinating children far outweigh any known risk of exposure to thitnerosal-containing vaccines.

As more information becomes available, the AAP will provide updates.

*Note that hepatitis B immune globulin (HBIG) products currently available in this country do not contain thimerosal.

COMMITTEE ON INFECTIOUS DISEASES, 1999-2000
Jon S. Abramson, MD, Chairperson
Carol J. Baker, MD
Margaret C. Fisher, MD
Michael A. Gerber, MD
H. Cody Meissner, MD
Dennis L. Murray, MD
Gary D. Overturf, MD
Charles G. Prober, MD
Margaret B. Rennels, MD
Thomas N. Saari, MD
Leonard B. Weiner, MD
Richard J. Whitley, MD

EX-OFFICIO
Georges Peter, MD
Emeritus Red Book Editor
Larry K. Pickering, MD

Red Book Editor
Neal Halsey, MD, Immediate Past Chairperson, Committee on Infectious Diseases, 1995-1999
P. Joan Chesney, MD, Member, Committee on Infectious Diseases, 1993-1999
S. Michael Marcy, MD, Member, Committee on Infectious Diseases, 1993-1999

BIBLIOGRAPHY

  1. Clarkson TW. Mercury: Major issues in environmental health. Environmental Health Perspectives. l992;100:31-38
     
  2. Clarkson TW. The toxicology of mercury. Crit Rev Clin Lab Sci. 1997;34:369-403
      
  3. Yess NJ. US Food and Drug Administration Survey of Methylmercury in Canned Tuna. Journal of AOAC International 1993;76 (1)
     
  4. Shenker BJ, Guo TL, Shapiro IM. Low-level methylmercury exposure causes human T-cells to undergo apoptosis: evidence of mitochondrial dysfunction. Environ Res. 1998;77:l49-159
     
  5. Amin-Zaki L, Majeed MA, Elhassani SB, et al. Prenatal methylmercury poisoning: clinical observations over five years. Am J Dis Child. 1979;133:172-177
     
  6. Bakir F, Damlugi SF, Amin-Zaki L et al. Methylmercury poisoning in Iraq. Science.1973;181:230-241
     
  7. Amin-Zaki I, Elhassani 5, Majeed MA, Clarkson TW, Doherty RA, Greenwood M. Intrauterine methylmercury poisoning in Iraq. Pediatrics. 1974; 54:587-595.
     
  8. US Environmental Protection Agency. Mercury Study Report to Congress. Washington, D.C.: US Environmental Protection Agency: 1997. Document EPA-4521R-97-007
     
  9. Tollefson L, Cordle F. Methylmercury in fish: a review of residue levels, fish consumption and regulatory action in the United States. Environ Health Perspectives 1986;68:203-208
     
  10. ATSDR. Toxicological Profile for Mercury. Atlanta, GA : Agency for Toxic Substances and Disease Registry, 1999
     
  11. Grandjean P, Weihe P, White RF, et al. Cognitive deficit in 7-year-old children with prenatal exposure to methylmercury. Neurotoxicol Teratol. 1997;6:417-428
     
  12. Davidson PW, Myers GJ, Cox C, et al. Effects of prenatal and postnatal methylmercury exposure from fish consumption on neurodevelopment: outcomes at 66 months of age in the Seychelles Child Development Study. JAMA. 1998;280:701-707
     
  13. Lucier G, Goyer R. Report of the Workshop Proceedings of Conference Organized by Committee on Environment and Natural Resources and the Office of Science and Technology Policy The White House: November 18-20. Published by the National Institute of Environmental Health Sciences
     
  14. Stern AH. Estimation of the interindividual variability in the one-compartment pharmacokinetic model for mercury: implications for the derivation of a reference dose. Regul Toxicol Pharmacol. 1 997:25;277-288
     
  15. Keith LH, Walters DB. The National Toxicology Program’s Chemical Data Compendium, Vol I-VIII. Boca Raton, FL: Lewis Publishers, Inc. , 1992
     
  16. Cox NH, Forsyth A. Thiomersal allergy and vaccination reactions. Contact Dermatitis 1988;18:229-233
     
  17. Axton JH. Six cases of poisoning after a parenteral organic mercurial compound (Merthiolate). Postgrad Med J. 1 972;561 :417-421
     
  18. Fagan DG, Pritchard JS, Clarkson TW, Greenwood MR. Organ mercury levels in infants with omphaloceles treated with organic mercurial antiseptic. Arch Dis Child. l977;52:962-964
     
  19. Matheson DS, Clarkson TW, Gelfand EW. Mercury toxicity (acrodynia) induced by long-term injection of gammaglobulin. J Pediatr. 1 980;97: 153-155
     
  20. Lowell JA, Burgess 5, Shenoy 5, Curci JA, Peters M, Howard TK. Mercury poisoning associated wit high-dose hepatitis-B immune globulin administration after liver transplantation for chronic hepatitis B. Liver Transpl Surg. 1996;2:475-478
     
  21. Pfab R, Muckter H, Roider 0, Zilker T. Clinical course of severe poisoning with thiomersal. J Toxicol Clin Toxicol. 1996;34:453-460
     
  22. 1999 Physicians Desk Reference. 53rd ed. Medical Economics Company
     
  23. American Academy of Pediatrics. In: Peter G, ed. 1997 Red Book: Report of the Committee on Infectious Diseases. 24th ed. Elk Grove Village, IL: American Academy of Pediatrics; 1997
     
  24. Gangarosa EJ, Galazka AM, Wolfe CR, et a]. Impact of anti-vaccine movements on pertussis control: the untold story. Lancet. l998;351:356-361
     
  25. Margolis HS, Alter MJ, Hadler SC. Hepatitis B: evolving epidemiology and implications for control. Seminars in Liver Disease. 199l;l 1:84-92
     
  26. Sell SH. Long-term sequelae of bacterial meningitis in children. Pediatr Infect Dis J. 2:90-93, 1983

Acknowledgement: The Academy would like to express its gratitude for the timely technical assistance provided by the Center for Biologics and Related Products of the FDA and the following individuals: Jim Lemons, Chairperson, AAP Committee on Fetus and Newborn, Michael Speer, AAP Committee on Fetus and Newborn, Robert Ward, Chairperson, AAP Committee on Drugs, Jack Swanson, Chairperson, AAP Committee on Practice and Ambulatory Medicine, Jan Berger, Chairperson, AAP Committee on Medical Liability, Thomas Clarkson (Rochester University), Barry Rumack (University of Colorado), Samuel Katz (Duke University), Thomas Burke, Nga Tran, Carlton Lee, and Lynn Goldman (Johns Hopkins University), and Ellen Silbergeld (University of Maryland).

Disclaimer: Please note in order to post this interim report as soon as possible, this document has not been copy-edited and the references have not been verified. The AAP will replace this document with the copy-edited version in the near future. In addition, this interim report will be published in an upcoming issue of AAP News and Pediatrics.

The recommendations in this statement do not indicate an exclusive course of treatment or serve as a standard of medical care. Variations, taking into account individual circumstances, may be appropriate.

Copyright © 1999 by the American Academy of Pediatrics

No part of this statement may be reproduced in any form or by any means without prior written permission from the American Academy of Pediatrics except for one copy for personal use.

+JuIy 14, 1999—FINAL
IMPLEMENTATION GUIDANCE FOR IMMUNIZATION GRANTEES DURING
THE TRANSITION PERIOD TO VACCINES WITHOUT THIMEROSAL
CENTERS FOR DISEASE CONTROL AND PREVENTION

 I. Purpose

This guidance is intended to assist immunization grantee program staff through a temporary transition period during which vaccine manufacturers are working to reduce or eliminate thimerosal from their products in accordance with recommendations contained in the Joint Statement of the Public Health Service (PHS) and the American Academy of Pediatrics (AAP) regarding thimerosal in vaccines (MMWR 1999; 48:563-565). A return to current recommendations is anticipated as soon as adequate supplies of thimerosal-free vaccines are available.

II. Background

On July 7, 1999, the American Academy of Pediatrics and the Public Health Service released a joint statement regarding thimerosal in vaccines (Appendix I) which was published in the MMWR. The AAP and the CDC have been developing guidance materials for their constituents. The AAP guidance was issued on July 12, 1999 (Appendix II) entitled "Thimerosal in Vaccines—An Interim Report". This CDC Interim Guidance document takes into consideration both the AAP/PHS Statement and the AAP Interim Report and provides additional information of interest to local and state immunization programs and health care providers participating in the Vaccines For Children program. This guidance also provides an Appendix of Questions and Answers developed by CDC regarding thimerosal that may be helpful in answering questions about programmatic issues (Appendix III)

III. Key Messages from the Joint Statement

The major points in the Joint Statement of the American Academy of Pediatrics and the Public Health Service are:

  1. Thimerosal has been used as an additive to biologics and vaccines since the 1930’s because it is very effective in killing bacteria used in several vaccines and in preventing bacterial contamination, particularly in opened multi-dose containers. Thimerosal constains a small amount of mercury in the form of ethyl mercury.
     
  2. The large risks of not vaccinating children far outweigh the unknown and probably much smaller risk, if any, of cumulative exposure to thimerosal-containing vaccines over the first six months of life.
     
  3. There are no guidelines for ethyl mercury, but experts agree that methyl mercury guidelines are appropriate to use in this situation. There is a significant safety margin incorporated into all Federal guidelines on methyl mercury exposure.
     
  4. There is no evidence of any harm caused by the level of exposure that some children may have encountered in following the existing immunization schedule.
     
  5. The Public Health Service, the American Academy of Pediatrics, and vaccine manufacturers agree that the use of thimerosal as a preservative should be removed as soon as possible.
     
  6. Clinicians and parents are encouraged to immunize all infants even if the choice of individual vaccine products is limited for any reason
     
  7. The recommendations remain unchanged for routine vaccination with DTaP/DTP, Hib, and for hepatitis B vaccination of infants born to hepatitis B surface antigen (HBsAg) positive mothers or mothers whose HBsAg status is unknown. All products are acceptable including those which contain thimerosal.
     
  8. Clinicians and parents can take advantage of the existing flexibility in the immunization schedule to delay hepatitis B vaccination from birth until two to six months for infants born to mothers who are HBsAg negative. More details are offered below.

IV. Guidelines

For Hib and DTaP/DTP

The PHS and AAP continue to recommend that all children should be immunized against diseases indicated in the recommended immunization schedule. Clinicians and parents are encouraged to immunize all infants even if the choice of individual vaccines is limited for any reason.

The use of products containing thimerosal is preferable to withholding vaccinations which protect against diseases that represent immediate threats to young infants (e.g. DTaP/DTP, Hib, and hepatitis B vaccine for infants at high risk for perinatal and early childhood hepatitis B virus infection.

For Hepatitis B

The Joint Statement makes suggestions for infant hepatitis B vaccination which take into account I) the age at the first dose, 2) the hepatitis B surface antigen (HBsAg) status of the mother, and 3) the birth weight and gestational age of the infant.

The Joint Statement reaffirms the recommendations for infants born to HBsAg positive mothers or for infants born to mothers whose HBsAg status is unknown. Therefore, these infants should continue to receive hepatitis B immunoprophylaxis as currently recommended and should receive hepatitis B vaccines as indicated. Currently, no thimerosal-free hepatitis B vaccines are licensed for use at birth. In populations where HBsAg screening of pregnant women is not routinely performed, vaccination of all infants at birth should be maintained, as is currently recommended.

Many hospitals have instituted policies to vaccinate all children at birth regardless of HBsAg status as a means of ensuring that all the infants of HBsAg positive women and infants of women with an unknown HBsAg status are vaccinated at birth. These hospitals should continue current policies until procedures are or can be put in place to guarantee the proper management of all births to prevent perinatal HBV transmission. Such procedures should ensure that 1) the HBsAg status of every pregnant woman is available and reviewed at delivery, 2) appropriate passive-active immunoprophylaxis (hepatitis B immune globulin [HBIG] and hepatitis B vaccine) is provided for infants of HBsAg positive women within 12 hours of birth, and 3) appropriate active immunoprophylaxis (hepatitis B vaccine) is provided for infants of women with an unknown HBsAg status.

Pregnant women whose HBsAg status is unknown at delivery should have their blood drawn for testing as soon as possible. If test results cannot be obtained within 12 hours of birth, the infant should be vaccinated. Infants of women determined to be HBsAg positive should receive HBIG as soon as possible but within 7 days of birth.

The AAP/PHS Joint Statement and the AAP Interim Report currently do not contain a statement about hepatitis B vaccination for infants born to HBsAg negative women from populations at increased risk of perinatal and early childhood HBV infection.

This CDC Interim Guidance expands on those statements and recommends that hepatitis B vaccination be carried out for infants born to HBsAg negative mothers belonging to populations or groups that have a high risk of early childhood HBV infection, including Asian Pacific Islanders, immigrant populations from countries in which HBV is of high or intermediate endemicity (see Health Information for International Travel, 1999), and households with persons with chronic HBV infection (HBsAg -positive persons). These infants should receive hepatitis B vaccine at birth.

The Joint Statement emphasizes the existing flexibility in the hepatitis B vaccination schedule for infants born to known or documented HBsAg-negative mothers in order to reduce cumulative exposure to thimerosal. It states: "Clinicians and parents can take advantage of the flexibility within the existing schedule for infants born to hepatitis B surface antigen negative women to postpone the first dose of hepatitis B vaccine from birth until two to six months of age when the infant is considerably larger."

If a decision is made to delay the birth dose of hepatitis B vaccine for infants of HBsAg negative mothers, the CDC prefers that hepatitis B vaccine be administered according to current recommendations of the Advisory Committee on Immunization Practices beginning at two months which is at the lower end of the the 2-6 month age range included in the AAP/PHS Joint Statement.

The Academy of Pediatrics supports the Joint Statement policy but prefers the administration of the first dose of hepatitis B vaccine at two months only if a thimerosal free vaccine is available. If it is not available, the AAP prefers that the first dose of hepatitis B vaccine be administered at six months.

The Joint Statement contains a precaution about vaccination of premature or low birth weight infants. It states that preterm infants born to HBsAg-negative mothers should receive hepatitis B vaccine, but ideally not until they reach term gestational age and a weight of at least 5.5 lbs (2.5 kg).
 

FINAL

July 7, 1999 4:15 PM

JOINT STATEMENT OF THE AMERICAN ACADEMY OF PEDIATRICS (AAP) AND THE
STATES PUBLIC HEALTH SERVICE (PHS)

The Food and Drug Administration (FDA) Modernization Act of 1997 called for the FDA to review and assess the risk of all mercury containing food and drugs. In line with this review, U.S. vaccine manufacturers responded to a December 1998 and April 1999 FDA request to provide more detailed information about the thimerosal content of their preparations which include this compound as a preservative. Thimerosal has been used as an additive to biologics and vaccines since the 1930s because it is very effective in killing bacteria used in several vaccines and in preventing bacterial contamination, particularly in opened multi-dose containers. Some but not all of the vaccines recommended routinely for children in the United States contain thimerosal.

There is a significant safety margin incorporated into all the acceptable mercury exposure limits. Furthermore, there are no data or evidence of any harm caused by the level of exposure that some children may have encountered in following the existing immunization schedule. Infants and children who have received thimerosal-containing vaccines do not need to be tested for mercury exposure.

The recognition that some children could be exposed to a cumulative level of mercury over the first six months of life that exceeds one of the federal guidelines on methyl mercury now requires a weighing of two different types of risks when vaccinating infants. On the one hand, there is the known serious risk of diseases and deaths caused by failure to immunize our infants against vaccine-preventable infectious diseases; on the other, there is the unknown and probably much smaller risk, if any, of neuro-developmental effects posed by exposure to thimerosal. The large risks of not vaccinating children far outweigh the unknown and probably much smaller risk, if any, of cumulative exposure to thimerosal containing vaccines over the first six months of life.

Nevertheless, because any potential risk is of concern, the Public Health Service, the American Academy of Pediatrics, and vaccine manufacturers agree that thimerosal-containing vaccines should be removed as soon as possible. Similar conclusions were reached this year in a meeting attended by European regulatory agencies, the European vaccine manufacturers, and the US FDA which examined the use of thimerosal-containing vaccines produced or sold in European countries.

The US Public Health Service and the American Academy of Pediatrics are working collaboratively to assure that the replacement of thimerosal-containing vaccines takes place as expeditiously as possible while at the same time ensuring that our high vaccination coverage levels and their associated low disease levels throughout our entire childhood population are maintained. 

The key actions being taken are:

  1. A formal request to manufacturers for a clear commitment and a plan to eliminate or reduce a expeditiously as possible the mercury content of their vaccines.
     
  2. A review of pertinent data in a pubtic workshop.
     
  3. Expedited FDA review of manufacturers’ supplements to their product license applications to eliminate or reduce the mercury content of a vaccine.
     
  4. Provide information to clinicians and public health professionals to enable them to communicate effectively with parents and consumer groups.
     
  5. Monitoring immunization practices, future immunization coverage, and vaccine-preventable disease levels.
     
  6. Studies to better understand the risks and benefits of this safety assessment 

The PHS and AAP continue to recommend that all children should be immunized against the diseases indicated in the recommended immunization schedule. Given that the risks of not vaccinating children far outweigh the unknown and much smaller risk, if any, of exposure to thimerosal-containing vaccines over the first six months of life, clinicians and parents are encouraged to immunize all infants even if the choice of individual vaccine products is limited for any reason.

While there is a margin of safety with existing vaccines containing thimerosal, there are steps that can be taken to increase that margin even further. Clinicians and parents can take advantage of the flexibility within the existing schedule for infants born to Hepatitis B surface antigen (HbsAg)-negative women to postpone the first dose of hepatitis B vaccine from birth until two to six months of age when the infant is considerably larger. Pre-term infants born to HbsAg-negative mothers should similarly receive hepatitis B vaccine, but ideally not until they reach term gestational age and a weight of at least 2.5 kilograms. Because of the substantial risk of disease, there is no change in the recommendations for infants of HbsAg-positive mothers or of mothers whose status is not known.

Also, in populations where HbsAg screening of pregnant women is not routinely performed. vaccination of all infants at birth should be maintained, as is currently recommended.

In addition to the key actions mentioned above, the P115 Advisory Committee on Immunization Practices (ACIP) and the AAP Committee on Infectious Diseases will be reviewing these issues and may make additional statements.

END OF JOINT STATEMENT

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