Date: March 12, 2003 Contacts: Christine Stencel, Media Relations Officer Cory Arberg, Media Relations Assistant Office of News and Public Information (202) 334-2138; e-mail <email@example.com>
For Immediate Release
SIDS Not Linked to Number and Variety of Childhood Vaccines
WASHINGTON -- The evidence does not support a causal link between sudden infant death syndrome (SIDS) and either the diphtheria, tetanus, and whole-cell pertussis (DTwP) vaccine or exposure to multiple childhood vaccines, says a new report from the Institute of Medicine of the National Academies. Only an older version of a vaccine against diphtheria and pertussis that is no longer administered to infants is causally related to fatal anaphylaxis, a rare and severe inflammatory reaction. These and other findings about childhood vaccines, SIDS, and other types of sudden unexpected death in infancy (SUDI) do not warrant a review of the childhood vaccination schedule, the report concluded.
"Although the timing of infant vaccinations coincides with the period when SIDS is most likely to occur, parents should rest assured that the number and variety of childhood vaccines do not cause SIDS," said Marie McCormick, chair of the committee that wrote the report and professor and chair, department of maternal and child health, Harvard School of Public Health, Boston. "We do not have the data that would definitively answer all questions about links between vaccines and SIDS and other forms of sudden, unexpected death in infancy. However, we believe that the data we do have, along with the increasing rarity of these kinds of infant deaths, make a review of the vaccine schedule unnecessary."
American children routinely receive five vaccines against seven infectious agents before age 1: the DTaP vaccine -- which contains a different form of the pertussis component than DTwP, which it replaced in the United States in 1997 -- and vaccines against Haemophilus influenzae type b, hepatitis B (HepB), polio, and pneumococcal bacteria. Although HepB is given to newborns, the others typically are administered at 2 months of age, with additional doses of certain vaccines given at 4 and 6 months.
SUDI encompasses sudden, unexpected deaths in which there may or may not be a clear cause of death. SIDS is the diagnosis most often given for infant deaths that occur without warning and for which no cause is identified. Medical researchers have not reached consensus on the risk factors for SIDS or how it occurs, although current guidelines to place babies on their backs or sides to sleep are based on theories that the prone position may contribute to SIDS. Another possible explanation, the "triple-risk" hypothesis, postulates that SIDS may occur through the interaction of an underlying biological vulnerability, a critical development period, and exposure to an outside trigger. It has been speculated that vaccination may act as such a trigger. Further research could show that there are many causes of SIDS.
Evidence from studies based on human exposure is strong enough to favor rejection of any causal connection between SIDS and multiple doses of different vaccines. In addition, the report reaffirmed previous findings that SIDS is not linked to the older DTwP. Because the currently used DTaP vaccine has fewer side effects than DTwP, the committee found no reason to suspect any link between DTaP and SIDS. However, without sufficient or adequate evidence available, the committee could not definitively reject a link between DTaP and SIDS. Evidence was also insufficient or inadequate to determine whether relationships exist between other individual vaccines and SIDS.
Although some research suggests that an abnormal immune response to common respiratory bacteria or viruses may be a factor in SIDS, there are no studies demonstrating the ability of vaccines to provoke abnormal inflammatory responses of the kinds seen in some SIDS cases. The committee concluded that the ability of vaccines to act as triggers of SIDS is only theoretical. A similar conjecture that fever or other common side effects of vaccination could spur an acute metabolic reaction in babies with an innate metabolic condition is also theoretical.
Although very rare, anaphylaxis from any cause -- such as a food, drug, or environmental allergen -- can lead to sudden, unexpected death. On the basis of a well-documented case of fatal anaphylactic shock in twin babies that occurred after each received a second dose of diphtheria toxoid and whole-cell pertussis vaccine (DwP), the committee concluded that the evidence favors acceptance of a link between this vaccine and infant death due to anaphylaxis. The case occurred in 1946, however, and the committee did not find any other well-documented reports of infant deaths related to anaphylaxis following vaccination, despite the widespread use of childhood vaccines during the 57 years since that case. Moreover, DwP is no longer used in the United States.
While the number and variety of vaccines infants receive is not linked to SIDS, there is not enough evidence to determine whether exposure to multiple different vaccines is causally linked to SUDI in general. Evidence also is not sufficient or adequate to determine if HepB, the only vaccine given to newborns, is linked to neonatal deaths, the report says.
A standard definition of SUDI should be developed, and criteria related to SIDS and SUDI should be consistently applied for research and reporting purposes. Comprehensive postmortem work-ups should be performed on all infants who die suddenly and unexpectedly, the report says.
The number of infant deaths declined between 1990 and 2000, dropping from 9.2 deaths per 1,000 live births to 6.9 per 1,000, the lowest infant mortality rate ever recorded in the United States. Because SUDI are difficult to define, there are no data on the national rate of SUDI in the United States. SIDS is the leading diagnosis for postneonatal death -- death occurring after the first 27 days -- and there were 2,523 deaths attributed to SIDS in the United States in 2000. The rate of SIDS has been declining over the past several years.
This study is the sixth in a series of eight on vaccine safety sponsored by the Centers for Disease Control and Prevention and the National Institute of Allergy and Infectious Diseases. The Institute of Medicine is a private, nonprofit institution that provides health policy advice under a congressional charter granted to the National Academy of Sciences. A committee roster follows.