- Knowledgebase: Immunization Questions
- Questions about immunizations, side effects, and not vaccinating.
- 6. The Stubborn Facts of Vaccine Safety - Top
- The Stubborn Facts of Vaccine Safety
Pediatric Annals 30:7 July 2001
Sharon G. Humiston, MD, MPH
The facts of vaccine safety are stubborn indeed. It takes years of careful research to find them, but then the facts have a way of hiding again in scientific reports. Of course, once grasped, facts are stubborn in another sense„Ÿthey are durable and persistent.
The facts of vaccine safety are of great concern to parents, health care providers, and public health administrators. Concern centers on both actual safety„Ÿwe are all working to optimize the well-being of our children„Ÿand perceived safety. If parents lose confidence in vaccination, that fear, even if unfounded, could lead to decreased immunization coverage and, consequently, to rising rates of disease. It is difficult to maintain public confidence in vaccines. The rare "one-time-in-a-million" reaction to vaccination can happen because huge numbers of children„Ÿvirtually the entire birth cohort of four million American children„Ÿwill receive the vaccine. No serious reaction is considered acceptable because this is, after all, preventive medicine given to otherwise healthy children. Additionally, vaccines are man-made, often considered involuntary, and given under memorable circumstances, all of which increases our sense of their inherent risk.
Years ago, medical and public health groups were not getting vaccine information on the Internet and to the press at anything like the rate that the anti-vaccine groups were getting out their perspective. That has changed now, but many misconceptions took root during our silence.
Indeed, a telephone survey of 1,600 parents4 showed that 25% thought too many immunizations could weaken a child's immune system. Twenty-three percent believed that children receive more immunizations than necessary. Nineteen percent felt that immunizations are not always proven safe before being approved for use. For parents in your practice who need a better understanding of the many layers of pre-licensure testing and regulation, this issue of Pediatric Annals offers a clear and straightforward article on this topic by Macartney and Offit.
Recently, while hosting television broadcasts and telephone conferences, I have heard the "call-in" questions of many health care providers. I would like to share with you the most frequent questions and either answer them or point you to the answers in this issue or the June issue of Pediatric Annals.
DO VACCINES OVERLOAD THE IMMUNE SYSTEM?
Vaccines contain few antigens compared with the barrage of germs an infant encounters in the cleanest of homes.5 A fact sheet from the Vaccine Education Center at The Children's Hospital of Philadelphia puts it succinctly:
In fact, babies are capable of responding to millions of different viruses and bacteria because they have billions of immunologic cells circulating in their bodies. Therefore, the vaccines given in the first two years of life are literally a raindrop in the ocean of what an infant's immune system successfully encounters in the environment every day.
DOES THE MERCURY IN THIMEROSAL (A VACCINE PRESERVATIVE) CAUSE BRAIN
DAMAGE?
Excessive mercury exposure can lead to brain and kidney damage. Because the unborn fetus is particularly susceptible, three federal agencies have developed guidelines, which leave a margin for safety, regarding how much methyl mercury a fetus could be exposed to with out suffering any known health effect. Because each guideline was developed using a different method, they differ. The Food and Drug Administration (FDA) considers 0.4 ,ug/kg/d of mercury safe, the Agency for Toxic Substance & Disease Registry (ATSDR) considers 0.3 ug/kg/d safe, and the Environmental Protection Agency (EPA) considers 0.1 ug/kg/d safe.
Thimerosal is a mercury-containing preservative that was in some brands of vaccines against diphtheria, tetanus, and pertussis (DTP); Haemophilus influenzue type b (Hib); hepatitis A; hepatitis B; and influenza. (It is not used in live vaccines such as measles- mumps-rubella [MMR] and varicella.) Therefore, vaccines became a focus of the recent FDA review.
Many toxicologists believe that ethyl mercury (the kind in thimerosal) is much less toxic than methyl mercury and that infants metabolize mercury differently from the way that fetuses do. However, no ethyl mercury guidelines were available for infants, so the FDA extrapolated from the chronic fetal methyl mercury guidelines. The FDA found that if a small infant received vaccines containing thimerosal for each of his or her recommended vaccines, the infant could be exposed to total levels of ethyl mercury that would exceed the EPA (although not the FDA or ATSDR) guidelines.
The Public Health Service, the American Academy of Pediatrics (AAP), and pharmaceutical companies agreed that thimerosal should be removed from pediatric vaccines to reduce children's
exposure to mercury. Now, at least one formulation of all routine childhood vaccines is thimerosal-free. A listing of the mercury concentration in all vaccines licensed in the United States is available at www.vaccinesafety.edu / thi-table.htm.
The changes have reduced the potential exposure to mercury. Much research is now under way
to determine how long ethyl mercury from thimerosal stays in the bodies of young children and
what effect it has on their development. In one recent study, scientists at the University of Rochester Medical Center tested the blood mercury levels of 16 full-term infants shortly after
vaccination. They found that blood mercury levels in all of the infants tested were lower than
the level of maternal blood mercury believed to represent a health risk.8 The infants were found to rapidly excrete the ethyl mercury in their stool.
On July 16, 2001, the Institute of Medicine, an independent panel of scientists from many fields, will hold a scientific meeting examining the available data on thimerosal and neurodevelopmental disorders. To learn more about this meeting, contact the Immunization Safety Review Committee at www.iom.edu/iom / iomhome.nsf / pages /
immunization+safety+review.
CAN WE SAFELY GIVE HEPATITIS B VACCINE AT BIRTH?
July 1999, the U.S. Public Health Service, the AAP, and the vaccine manufacturers announced that pediatric vaccines containing thimerosal should be removed from the U.S. market. The birth dose of hepatitis B vaccine (given at birth, when the body weight is lowest and, thus, the mercury exposure per kilogram of body weight is highest) was the first priority. While a thimerosal-free version of the vaccine was in development, hepatitis B vaccination of newborns (with hepatitis B-negative mothers) was temporarily suspended. Within 2 months, a thimerosal-free formulation of hepatitis B vaccine was available, and shortly thereafter both licensed pediatric hepatitis B vaccines no longer contained thimerosal as a preservative. In July 2000, the Centers for Disease Control and Prevention (CDC) published a notice that "efforts should be made to reintroduce routine hepatitis B vaccination policies for all newborn infants."
Health care providers should recognize that, because of the risks associated with both acute and chronic hepatitis B. it is critical that a birth dose of hepatitis B vaccine be given to infants born to mothers whose hepatitis B surface antigen is positive or unknown. Giving a birth dose of hepatitis B vaccine to the infant of a mother whose hepatitis B surface antigen is negative will increase the infant's likelihood of completing his or her hepatitis B immunization series on timely and is not associated with an increase in adverse reactions.
DO VACCINES CONTAIN THE "MAD COW" INFECTIOUS AGENT?
Bovine spongiform encephalopathy (BSE), also known as "mad cow disease," is a fatal disease of the nervous system of cows that was first diagnosed in 1986. Variant Creutzfeldt-Jakob disease (vCJD) is a disease of the nervous system of humans that begins with serious psychiatric problems or sensory problems and is later manifested by muscle spasms, loss of coordination, and confusion. On average, death follows the first symptoms of vCJD in approximately 13 months. Consumption of food contaminated with the BSE agent (which may be a modified cell protein) has been linked to vCJD in the United Kingdom, Ireland, and France.
In 1993, the FDA asked all vaccine manufacturers to eliminate bovine materials from countries affected by BSE, but recently FDA officials discovered that some vaccine manufacturers were not strictly following these recommendations. For this reason, the FDA convened a meeting of BSE and vaccine experts on July 27, 2000. After taking many factors into account (eg, the number of infected animals, the concentration of infectious units in infected animal blood, and the amount of blood used per dose of vaccine), they estimated the risk of vCJD from the use of European bovine-derived materials to be 1 in 2 billion doses for a bacterial toxoid or 1 in 40 billion doses for a viral vaccine. Officials noted that no cases of vCJD have been attributed to vaccine use and that there is no evidence that any vaccine actually contains the BSE agent.
Researchers in Britain have found that, of the original 52 British cases of vCJD (all of the cases that were diagnosed at the time of the study in October 2000), 49 patients were born before 1930 and, therefore, would have received the vaccines before BSE emerged. The other 3 patients with vCJD were born in the 1980s, so they were not exposed to the disease through vaccination because the vaccines used for them also were manufactured with bovine materials obtained before 1936. This study eliminates concern that the original 52 British cases of vCJD were vaccine related, but it does not eliminate the possibility that a person could get vCJD from immunization some day.
The CDC has responsibility for vCJD surveillance in the United States and, to date, this surveillance shows no vCJD. To keep the U.S. public safe, the FDA sent a letter to manufacturers in April 2000 requesting that they stop using any materials derived from European ruminants (eg, cows or sheep) in FDA-regulated products for humans. The concerns about the theoretical risks of vCJD infection through vaccines have resulted in additional scrutiny of vaccine manufacturing processes. A current list of vaccines using bovine-derived materials from countries on the U.S. Department of Agriculture BSE list or from countries in which the status of BSE is unknown can be found at www.fda.gov / cber / bse / bse.htm#usda. Scientists will continue to study how the BSE agent can be transmitted to humans, but the facts reassure health care professionals that the risk of BSE contamination of vaccines is miniscule compared with the risk of physical disability, mental damage, or death from infectious diseases such as Hib, diphtheria, or tetanus.
SHOULD WE USE UP OUR SUPPLY OF ORAL POLIO VACCINE?
Because of the true causal association between oral polio vaccine and paralytic polio, oral polio vaccine is no longer recommended for routine childhood immunization.l4 The switch to an all-inactivated polio vaccine schedule has not decreased polio immunization coverage in the United States; parents are willing to accept the injection for the sake of safety.
DO VACCINES CAUSE SUDDEN INFANT DEATH SYNDROME?
The Institute of Medicine reviewed the evidence and concluded that DTP did not cause sudden infant death syndrome. The incidence of sudden infant death syndrome has actually decreased during the time period when hepatitis B vaccine has been given to infants routinely. However, this decrease is probably due to the AAP's "Back to Sleep Program," an effort to get parents to put infants to sleep on their backs.
DOES HEPATITIS B VACCINE CAUSE MULTIPLE SCLEROSIS?
In 1994, the Institute of Medicine published a review of the evidence showing that vaccines did not cause diseases of the nervous systemic Subsequent reviews by the World Health Organization and the National Multiple Sclerosis Society came to the same conclusion. Recent studies have shown no association between hepatitis B vaccination and multiple sclerosis. A controlled study of individuals reporting demyelinating diseases to the Vaccine Adverse Event Reporting System also failed to show an association between hepatitis B vaccination and either multiple sclerosis or optic neuritis.
DOES THE HIS VACCINE CAUSE DIABETES?
Finish researchers have shown that the rates of type I diabetes in Hib-vaccinated and unvaccinated children were not different. In 1999, the Diabetes Workshop Panel of the Institute for Vaccine Safety concluded that "no vaccines have been shown to increase the risk of type I diabetes in humans."
IN MY PRACTICE, IT SEEMS THAT THE DIPHTHERIA AND TETANUS TOXOIDS AND ACELLULAR PERTUSSIS (DTAP) VACCINE CAUSES FEWER ADVERSE REACTIONS THAN THE DTP VACCINE DID. ARE THERE DATA ON THIS?
Reports to the Vaccine Adverse Event Reporting System concerning serious adverse events believed to be caused by whole-cell pertussis vaccine have declined.26 Common mild side effects (eg, fever or local soreness) are less common after acellular pertussis vaccine than after whole-cell pertussis vaccine, but temporary swelling of the entire limb has been noted in some children who receive DTaP boosters.
DOES THE MMR VACCINE CAUSE AUTISM? WHAT SHOULD I TELL PARENTS WHO WANT THEIR CHILD TO RECEIVE THESE THREE ANTIGENS GIVEN SEPARATELY?
The article by Kastner and Gellin in this issue of Pediatric Annals contains a full discussion of the MMR vaccine and autism.
HOW SHOULD I RESPOND TO QUESTIONS ON CONTRAINDICATIONS TO VACCINATION?
In this issue, Bahta et al. provide guidance on the true contraindications to vaccination. Please note that allergy to eggs is no longer considered a contraindication to the MMR vaccine.
WHAT DO YOU SAY TO PARENTS WHO WANT TO WAIT BEFORE VACCINATING THEIR CHILD?
Waiting to vaccinate is not a neutral, risk-free stance. All parents (and providers) should read the article in this issue about one family that put off making this serious decision.
HOW SHOULD I RESPOND TO QUESTIONS ON THE TIMING AND SCHEDULING OF VACCINES?
The most common questions that I am asked relate to the timing and scheduling of vaccines. The article by Humiston and Strikas in the June issue of Pediatric Annals provides information on this complex topic. Questions regarding the catchup schedule for pneumococcal conjugate vaccine are also addressed by Baiter and Van Beneden in that issue.
HOW SAFE IS THE PNEUMOCOCCAL CONJUGATE VACCINE?
Baiter and Van Beneden review this topic in detail in the June issue of Pediatric Annals. In the first 9 months of distribution of the new vaccine, Vaccine Adverse Event Reporting System forms were consistent with expected side effects already appreciated before licensure.
WHAT SHOULD WE TELL PARENTS ABOUT THE RISK OF MENINGOCOCCAL DISEASE AND THE VACCINE?
Recent outbreaks of meningococcemia have parents worried. Dull and Rosenstein review meningococcal disease and prevention through vaccination in the June issue of Pediatric Annals.
WILL VARICELLA VACCINE LEAD TO WANING IMMUNITY AND SERIOUS DISEASE LATER IN LIFE?
A huge number of providers have expressed their concern and confusion about the long-term effects of varicella vaccination. The article by Watson in the June issue of Pediatric Annals discusses this further.
WHAT WEB SITES DO YOU RECOMMEND FOR PARENTS WHO WANT TO KNOW MORE ABOUT VACCINES?
Fredrickson et al. explain in their article in this issue of Pediatric Annals that we need to layer information for parents, giving them as much as they need without overwhelming the faintly curious. The Internet is often a good tool for this. To me, the single best web site is www.vaccine.org because it is actually seven sites, including the AAP, the Immunization Action Coalition, the National Network for Immunization Information, the Vaccine Education Center at The Children's Hospital of Philadelphia, and Parents of Kids with Infectious Diseases. Other web sites include those of Johns Hopkins University (www.vaccinesafety.edu), the CDC (www.cdc.gov / nip /vacsafe), and the FDA (www.fda.gov).
WHAT OTHER TOOLS DO YOU RECOMMEND FOR PARENTS WHO WANT TO KNOW MORE ABOUT VACCINES?
The CDC's Vaccine Information Statements (VISs) are one page documents that answer most of the questions that parents have about specific vaccines (eg, What are the benefits? What are the common side effects? What are the potential severe side effects?). The article by Wolfe in this issue of Pediatric Annals provides a full description of their use.
Parents who want additional print material can be referred to other sources, including a one page "Q & A" fact sheet by the Vaccine Education Center at The Children's Hospital of Philadelphia (215-590-9990 or vaccines~email.chop.edu.); a set of immunization information sheets produced by the National Network for Immunization Information (877-341- 6644); an immunization booklet called The Parents' Guide to Immunizations produced by the National Immunization Program of the CDC (www.cdc.gov / nip); and two books on vaccines, Vaccinating Your Child:Questions and Answers for the Concerned Parent (Humiston and Good) and Vaccines: What Every Parent Should Know (Offit and Bell) that are available through bookstores and web sites. For parents who would benefit from a videotape on vaccine safety, there is "Vaccines: Separating Fact from Fear" by the Vaccine Education Center at The Children's Hospital of Philadelphia (215-590-9990 or vaccines~email.chop.edu). This videotape is not only informative, but also emotionally compelling because of the stories of parents who have lost or almost lost children to vaccine-preventable diseases.
HOW CAN PARENTS, MY STAFF, AND I GET OUR NEXT QUEST10N ANSWERED?
The most comprehensive service for answering vaccine questions is provided by the CDC National Immunization Program's National Immunization Hotline, which can be reached by telephone (1-800-232-2522) or e-mail (nipinfo~cdc.gov).
THE BEGINNING
It takes more time to developthe scientific evidence on vaccine risks and benefits than it does to develop fear and doubt. It takes more time to build trust and open communications than to destroy them. We do not live in an era of unquestioning reverence for vaccines, so we must develop the science to evaluate vaccine safety and the skills to communicate the results or we will return to the problems of an earlier age. We have only just begun.
1. Henry LC, ed. Best Quotations for All Occasions. Greenwich, CT: Fawcett Publications; 1986.
2. Gangarosa EJ, Galazka AM, Wolfe CR, et al. Impact of anti-vaccine movements on pertussis control: the untold story. Lancet. 1998;351:356-361.
3. Sandman PM. Responding to Community Outrage: Strategies for Effective Communication. Fairfax, VA: American Industrial Hygiene Association; 1993.
4. Gellm BG, Maibach EW, Marcuse EK, et al. Do parents understand immunizations? A national telephone survey. Pediatrics. 2000;106:1097-1102.
5. McPhillips H. Marcuse EK. Vaccine safety. Curr Probl Pediatr. 2001;31:91- 121.
6. Vaccine Education Center at The Children's Hospital of Philadelphia. Q ~ A: The Facts About Childhood Vaccines, vol. 2. Philadelphia: Vaccine Education Center at The Children's
Hospital of Philadelphia; 2001. Available at vaccine.chop.edu.
7. Ball LK, Ball R. Pratt RD. An assessment of thimerosal use in childhood vaccines. Pediatrics. 2001:107:1147- 1154.
8. Pichichero M, Clarkson T. Lopreiato J. Cernichiari E, Treanor J. Blood mercury levels in infants receiving vaccines containing thimerosal. Pediatr Res. 49(4), Part II of II, Abstract #1385.
9. Centers for Disease Control and Prevention. Update: expanded availability of thimerosal preservaUve-free hepatitis B vaccine. MMWR. 2000;49: 642, 651.
- Updated: July 11, 2001
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