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Do Immunizations Cause SIDS?

Sat, 23 Oct 1999

The studies showing no increased risk for SIDS with the DTP immunizations actually showed that fully immunized infants had a lower risk for SIDS. Although no study has yet explained this relationship, it is likely indirectly related to other risk factors like socioeconomic status (SES)-------babies fully immunized likely have good access to health care and higher SES than infants not up to date on immunizations, and may be more likely to be full term, etc.

Actually, there is an immune response of newborn infants to the hepatitis B vaccine. It is true, however, that starting this vaccine can safely be delayed to two months in low-risk infants------ASSUMING THAT THE BABY WILL RECEIVE WELL INFANT CARE. This theoretical risk from the mercury in the hepatitis vaccine is based on weight, and by two months of age the amount of mercury is below the federal threshold for concern.

As you stated, the rotovirus vaccine has been withdrawn pending the results of the study in progress. This was done because this infection does not result in serious consequences for most infants, even though it may require days at home for the infant and a parent. There were notices distributed by the American Academy of Pediatrics and the FDA, and articles in some newspapers, but the coverage was unfortunately not as complete as desired.

Hope this is helpful.
Dr. Hunt

Someone brought up some interesting questions about immunizations, how they might effect development of the immune system in infants, and whether there might be some indirect effect which could predispose to SIDS.

These are excellent questions. I do not think the final answers to all of them are known. However, let me try to deal with some of them.

I do not believe that there is any evidence suggesting that vaccines interfere with development of the normal immune system. The immune system of the infant is nearly a blank page. As he or she is exposed to things in the environment, when appropriate, anitbodies are made against them. Before immunizations existed, infants and young children were exposed to infectious agents and either developed immunity or died. The immunizations present these antigens to the infants in a "safe" way, such that immunity is generated rather than acquiring the illness. Therefore, immunizations seem to use a natural process which does not seem to interfere with the development of the immune system. I think there has been a lot of study on this.

I do not think there is any evidence that SIDS is caused by immune deficiency. The thymus, part of the immune system, in particular, has been studied in SIDS (as it was once thought to be a cause). Similarly, SIDS victims do not show evidence of excessive or unusual infections one might expect to see in someone with an immune deficiency.

There are some researchers investigating the possibility that immune response to certain types of organisms might affect respiratory control. These studies are intriguing. Although I would not consider them at the mainstream of SIDS research, I would encourage creative research in a variety of areas if it might shed some light on SIDS and speed its cure. However, the organisms being considered are not those currently being immunized against. Therefore, it is unlikely that immunizations will play into this potential mechanism.

Therefore, your questions show great insight, and continued study is important. However, to date, I do not think there is evidence that immunizations contribute to processes which might result in SIDS. Thank you for your thought provoking questions.

Thomas G. Keens, M.D.
Childrens Hospital Los Angeles

Reprinted with permission

A number of epidemiologic studies have now been performed which look into the possible relationship of SIDS and DTP immunizations. The majority of studies, and the better studies, do not show a relationship. SIDS is most common between 2-4 months of age. Immunizations are routinely given at 2 and 4 months of age. Thus, by chance alone, one in eight SIDS babies will have died within a week of their baby shot. However, the larger studies do not show any greater frequency of SIDS near immunizations. The NIH collaborative study actually showed that fewwer SIDS victims had baby shots than controls.

A number of years ago, our group took a different approach. We recorded the breathing pattern and heart rate of babies overnight the night before and after their DTP immunizations. We had three groups of infants: controls, SIDS siblings, and apnea of infancy (ALTE). There was no difference in the recordings the night after vs the night before the baby shot. In fact, there was a slight trend for breathing to be more regular after the baby shot.

These two pieces of information indicate that SIDS and/or apnea are not due to DTP immunizations.

A number of years ago, a rather vocal group persuaded many British mothers not to immunize their babies. The rate of pertussis (whooping cough) skyrocketed, and total deaths increased. Many more babies died from pertussis than would have died from the very infrequent reactions to the vaccines (less than 1 in 1,000,000). Pertussis is still widespread. Babies who are not immunized can catch it. We see several cases per year in Los Angeles. Pertussis can cause death in babies.

Therefore, in general, I urge all parents, and parents who have had babies die from SIDS, to have their babies immunized at the regular schedule (2, 4, and 6 months of age). There is little, if any, evidence suggesting that SIDS is due to immunizations. There is a great danger of a baby dying from other preventable diseases if not immunized.

For those interested, the following is an article I wrote on this topic for the California SIDS Program newsletter some time ago ...

Normally, infants receive their immunizations (baby shots) against pertussis (whooping cough), diphtheria, tetanus, polio, hepatitis, and hemophilus influenza (meningitis) at 2 and 4 months of age. SIDS also has its peak incidence between 2-4 months of age. So, the question naturally arises whether immunizations, specifically pertussis immunizations, might cause SIDS.

Even if there is no relationship between immunizations and SIDS, by chance alone, as many as one-in-eight SIDS victims will die within a week of their immunization. Thus, a large number of SIDS babies have died within days, or even hours, of their immunization. However, this does not necessary imply a cause. Currently, scientific evidence indicates that there is no relationship between immunizations and SIDS.

Several studies have been performed to determine the effect of DTP immunizations on SIDS. The majority of studies, and the better studies, do not show any relationship between SIDS and DTP immunizations.

We previously performed a study comparing recordings of the breathing pattern and heart rate in control infants, apnea babies, and SIDS siblings the night before and the night after the DTP immunization. There was no difference in the breathing pattern or heart rate after the baby shot. Thus, the immunization does not seem to cause abnormalities in breathing which might progress to death.

Several years ago, a vocal radical group in Great Britain convinced a large number of parents not to immunize their babies. The whooping cough (Pertussis) incidence markedly increased, and deaths due to whooping cough markedly increased to numbers much higher than the SIDS rate. Thus immunizations do prevent infection and save lives.

Unfortunately, the DTP immunization rarely causes severe neurologic problems. However, the risk of serious neurologic reactions to the DTP immunization is in the range of 1,000-times less frequent than the SIDS rate. Thus, this rare reaction is unlikely to cause such a relatively common problem (SIDS).

In summary, DTP immunizations do not cause SIDS. We recommend that all infants, even those at statistically increased risk for SIDS (such as some infants on home monitors) should receive their regular immunizations on the regular schedule at 2, 4, and 6-months. This provides the best overall protection for your baby.

Thomas G. Keens, M.D.
Childrens Hospital Los Angeles

Reprinted with permission

1) How early or late in pregnancy should an immunization be given to the mother in order to prevent disease in the baby? I am not advocating that mothers be immunized in order to prevent disease in babies. Certainly the live virus vaccines (measles, mumps, rubella, polio) might be dangerous to give during pregnancy, as they might actually infect the baby in the uterus. Mother's anitbodies against some diseases ordinarily cross the placenta into the baby and are present at birth. However, these only last until about 3-months of age. Immunizing the mother will not substantially change this.

2) If the mother has been immunized in her youth, would a booster shot help? A booster immunization to the mother during pregnancy would boost the amount of circulating anitbodies in the mother to the specific disease immunized against. Thus, there would potentially be more antibodies which cross into the baby. However, they would still be gone at about 3-months of age. Therefore, a booster immunization to the mother would probably not make much difference.

3) Would breast feeding extend a baby's immunity? Yes. Human milk contains anitbodies and lymphocytes which improve the baby's abilities to fight infections. Is this protection as much as is conferred by an immunizations? No.

4) Aside from immunization, what practices might help reduce the risk of infections? If one chooses to delay immunization (which I do not generally recommend, with the exception of babies who have had reactions as described in previous E-Mails), then one might want to be more careful about not exposing a baby to others. Keep the baby out of crowds. Do not take the baby out. Limit visitors, etc.

Thomas G. Keens, M.D.
Childrens Hospital Los Angeles

Reprinted with permission

Vaccinations have played a pivotal role in the prevention of contagious diseases and have been the major influence in the eradication of smallpox. Parents must continue to be encouraged to have their children vaccinated despite the fact that they are not risk-free. EVERYTHING we do in medicine has some side effect. In the case of vaccinations clearly the benefits out-weigh the risks. In addition the large collaborative NICHD study found NO correlation between vaccinations and SIDS; on the contrary MORE SIDS victims were DELAYED in their IMMUNIZATIONS than those that did not die. Immunizations are a mainstay of disease prevention and their use is increasing over time. We now have a vaccine against chickenpox. The AIDS vaccine has been trialed in animals. We must continue to have our children immunized. As a public service have your readers look at the AMA or American Academy of Pediatrics sites.

J D DeCristofaro, MD
Infant Apnea Program
Stony Brook, NY

Here are the correct data according to the "1994 Red Book: Report of the Committee on Infectious Diseases", published by the American Academy of Pediatrics (pp 361-364).

SEVERE ALLERGIC REACTIONS (Anaphylaxis): 2 per 10,000 doses. However, severe anaphylaxis "resulting in death, if any, are extremely rare".

SEIZURES (Convulsions): 1 per 1,750 doses. Seizures are brief, self limited, and occur in children with fevers.

COLLAPSE OR SHOCK-LIKE STATE: 3.5 to 291 per 100,000 doses. A recent follow-up study of these children showed that none developed evidence of serious neurologic damage or intellectual impairment.

SEVERE ACUTE NEUROLOGIC ILLNESS AND PERMANENT BRAIN DAMAGE: Considered to be "extremely rare", and no specific incidence figure was given. A case control study of children who were hospitalized encephalopathy showed no temporal relationship to the DTP immunization. Only 35 of 1,182 children with encephalitis had a DTP immunization within 1-week of onset.

The Red Book summarizes "The Committee concludes, based on currently available data, that pertussis vaccine has not been proven to be a cause of brain damage". It also concludes there is no relationship to SIDS.

One needs to compare the risks of pertussis immunization against the risks of pertussis infection. Also from the "1994 Red Book", Bordatella pertussis, the bacteria causing whooping cough, is carried by humans. Adults and older children are asymptomatic hosts for this bacteria. Adults and older children do not receive the pertussis vaccine after age 6 years, and consequently lose their immunity. However, pertussis infection is often asymptomatic in adults. Thus, pertussis is alive and well. 90% of non-immune household contacts acquire the disease. The mortality rate of pertussis in infants is 1.3%, ten-times the SIDS rate.

On balance, the risks of pertussis immunization seem less than the risks of pertussis infection. The new acellular vaccine should decrease these risks even further.

Thomas G. Keens, M.D.
Childrens Hospital Los Angeles

Reprinted with permission

Doctor Harris Coulter asked what I thought about his comments that DTP immunizations affect the sensory cranial nerves. He specifically mentions the vagus nerve as a possible factor in SIDS.

I have a few thoughts. The vagus nerve is a nerve which controls a number of automatic functions of the heart, lungs, intestinal tract, etc. It does slow heart rate, when stimulated. Absence of a vagal effect causes in increased heart rate. So-called, "vaso-vagal" reactions can be associated with profound heart rate slowing, and may be associated with so-called "breath holding spells" in older children. However, Doctor Coulter is suggesting a "cranial nerve palsy", or absence of vagal nerve input. This would presumably result in a rapid heart rate, not the heart stopping.

The vagus nerve also has a role in breathing. First, it is important to remember that the respiratory centers, located in the brainstem, primarily function from input from "chemoreceptors". These "measure" oxygen and CO2 in the blood, and stimulate or depress the central respiratory controllers to increase or decrease breathing, to adjust the oxygen and CO2 levels. These are the major determinants of breathing. The vagus is one of several secondary inputs into the respiratory controllers which modify breathing. Generally, vagal stimulation depresses breathing. Thus, a "cranial nerve palsy", if anything, would be expected to increase breathing.

Based on the above reasoning, I would not expect vagal nerve dysfunction to predispose to apnea (not breathing) or slow heart rate. Having said this, pathologists at the University of Toronto a number of years ago published a study suggesting decreased myelination of the vagal nerves in babies who died from SIDS compared to controls. Myelin is like the insulation around an extension cord. Delayed myelination means the nervous system may not work as well because of "short circuits".

Clearly, there is a great deal of research interest in brainstem function (respiratory controller) and vagal influences on the way heart rate is controlled. These studies are ongoing.

As to DTP immunizations, no one denies that reactions to vaccines occur. In fact, they have been carefully studied (and continue to be). I gave the statistics from the American Academy of Pediatrics' 1994 Red Book a week or so ago on this SIDS-Net. "Organized medicine" is not trying to suppress information about these. In fact, the Center for Disease Control and Prevention (CDC) keeps close track of immunization reactions, and is continually weighing their risks against the benefits of immunizations. The push for development of the acellular pertussis vaccine arises from this concern and surveillance. Other changes in vaccine practice are contemplated as well.

It sounds like some parents on this SIDS-Net may be describing reactions to an immunization which caused injury or death to your children. However, these reactions are fairly typical and reproducible, and appear distinct from SIDS. It has been suggested that "organized medicine" has ignored the relationship of SIDS to DTP immunizations. The contrary is clearly true. The age coincidence between SIDS and immunizations made this an important area for study. Many studies have, in fact, been reported in the medical literature. In general, these studies do not show a relationship. There are a few which do suggest a relationship. However, on balance, the majority of published studies do not.

There have been suggestions that reputable studies showing that DTP immunizations cause SIDS have not been able to be published. There are literally hundreds of medical journals. Scientific medical journals publish an article after "peer review". This means that a description of a scientific study is sent out to 2-4 reviewers, who are also scientists in the field. They critique the manuscript. The manuscript is usually sent back to the authors for rebuttal. The article is then accepted for publication in the journal, or rejected. Not all good articles are accepted. Some of my articles have not been accepted. But, if I felt strongly enough about the research we have done, I have submitted it to other journals until it was accepted. There is no organized "blackballing" of articles by reviewers. In fact, one reviewer is not even told who the other reviewers are, so the reviews are done independently. If any article is not published after repeated attempts, often it is because the science is suboptimal. There are enough "bad" articles that do make into press. Therefore, it would be difficult to postulate some sort of organized campaign to prevent an article from being published.

Thomas G. Keens, M.D.
Childrens Hospital Los Angeles

Reprinted with permission

Why is it that when a 10 pound newborn gets a vaccine, they get exactly the same dose as a 45 pound 5 year old? Would we do this with Tylenol? How is it possible that we have never subjected vaccines to a true placebo-controlled double-blind test - showing vaccinated against unvaccinated to show that they really don't cause this terrible damage and death to children? How is it that they can be defended so strongly when so little is really known about them?

Your questions are good ones, and illustrate why this subject has been so difficult to sort out and to explain. Although I cannot presume to speak for all pediatricians or all SIDS researchers, these are my briefly-stated answers. For those of you with good memories, Dr. Keens made the same points last March.

Over the years, many diseases or medical problems have been suggested as caused by the immunizations (baby shots) because both occurred in the same general time frame. Since most SIDS occurs in the 2-6 month age range and most babies get 3 shots during this time period, just by chance alone there will be instances when the 2 events occur close together (just by chance: 1 SIDS/1000 infants within 24 hours, and 12-13% within 1-2 weeks of the baby shot). The only way to sort this out, then, is by doing very large population-based statistical studies to determine whether the risk of SIDS was any different in babies of the same age and same risk factors not receiving immunizations compared to those who did get baby shots. All such studies, from several countries, have conclusively shown no relationship between immunizations and SIDS. Indeed, a 1995 report by Mitchell and others from New Zealand observed that the risk of SIDS was 50% less in the 4 days following immunization compared to matched infants not getting a baby shot.

The good news is that the newly approved pertussis (whooping cough) "acellular" vaccine has a much lower risk of the common mild-moderate reactions (like fever, drowsiness, fussiness). As a result, it is now possible in the U.S. to use the pertussis vaccine that has been used for a number of years in countries like Japan, and get the same or better resistance to these serious infections with significantly less chance of experiencing any of the recognized potential side effects of DPT. Again, however, SIDS is NOT one of these recognized potential side effects.

Extensive autopsy evaluations have been unable to detect ANY differences in infants recently immunized compared to those without recent (or any) baby shots.

I hope this is responsive to your questions.

Dr. Carl Hunt
Washington, DC/Toledo

March 24, 2004

Its been many years since I lost my children to SIDS. I lost two children, my first born, female, born 8/5/77 died 12/11/77.... she had colic pretty bad and I spent many nights up with her. She received are DPT the weds before she died, I always always thought this might have cause some kind of reaction. My 3rd child, born April 14, 1980 died may 25 1980. He also had received his first DPT shot right before he passed away ...  Even though it has been 27 years almost I still hurt for my children. I now have grandchildren and it is and always will be a number one worry in my heart and soul.... please let me know what you have on this.

March 24, 2004

SIDS tends to occur at a time (age range) when many immunizations are being given to infants. The age range of SIDS and the age range of frequent childhood immunizations overlaps. Therefore, it is expected that a significant proportion of SIDS deaths will occur following immunization. This has given rise to the belief that SIDS and immunizations are related, which is very understandable. However, many well-controlled large epidemiological studies have shown very clearly that there is no association between childhood immunizations and SIDS. In fact, several recent studies suggest that vaccines may have a protective effect with respect to SIDS. Thus, some babies diagnosed with SIDS do die right after vaccination, but multiple large studies have concluded that this is coincidence. The evidence indicates that vaccinations do not increase the probability of SIDS and do not play a causative role.

Best regards,
John Carroll, MD

March 24, 2004

When there has been a loss of multiple children to SIDS, I think one has to look hard for some inherited or environmental problem, such as a metabolic disorder. Despite unusual stories like this, the research stands, which does not show a relationship between SIDS and immunizations. Some studies show that SIDS victims were less likely to have been immunized than controls, suggesting that baby shots may be protective. Certainly, baby shots do protect against pertussis (whooping cough) and other disease which can, in and of themselves, cause infant deaths. During a period when many parents in the U.K. stopped giving immunizations following a radical news story, the incidence and death rate from pertussis went up --- far exceeding the expected SIDS rate. I have to say that there is often a tone of distrust among some parents who strongly advocate for delaying or avoiding baby shots. They seem to believe that the SIDS research community is attempting to hide information so that more babies would continue to die. Why would we do this? We are as committed as they are to stopping the tragedy of SIDS. So, from a scientific point of view, the best epidemiological evidence indicates that baby shots and SIDS are not related. In order to prevent deaths from other preventable diseases, babies should receive their baby shots at the current schedule (2, 4, and 6 months of age).

I hope this helps. Thank you.
---Tom Keens, MD


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