Dr. Paul A. Offit

Testimony toGovernment Reform Committee

Autism – Present Challenges, 
Future Needs – Why the Increased Rates?

April 6, 2000


My name is Paul Offit. I am a practicing pediatrician. I am also the Chief of Infectious Diseases and the Henle Professor of Immunologic and Infectious Diseases at The Children’s Hospital of Philadelphia and the University of Pennsylvania School of Medicine, and a member of the Advisory Committee on Immunization Practices to the CDC. I am also the co-author of a book entitled “Vaccines: What Every Parent Should Know”. My expertise is in the areas of virology and immunology.

In addition, I have been in collaboration with Merck and Co. on the development of a rotavirus vaccine since 1992. My interest in this project is to prevent rotavirus disease. In developing countries rotavirus infections kill about 14 children every day. In fact, more children die every day from rotavirus infections than from any other single infectious disease. In the United States, about 1 out of every 75 children born will be hospitalized with severe water loss (or dehydration) as a result of rotavirus infections. We hope that by developing this vaccine we can prevent the severe disease and death caused by this virus.

            My role in these proceedings is to explore the theories that have arisen due to concerns by the public that autism might be caused by the combination of measles, mumps, and rubella vaccines (known as MMR). No evidence exists that proves this association. However, three theories have been used to explain it. In the time that I have been given, I would like to explain why I think that these theories are not valid.

The first theory is that children who get the measles vaccine make an immune response not only to the vaccine, but also to their own nervous system. This kind of reaction is called autoimmunity. To understand why this theory is incorrect, we must first understand differences between natural measles infection and measles vaccination.

During natural measles infection, the measles virus reproduces itself many times in the body and causes disease. In contrast, following measles vaccination, the vaccine virus reproduces itself much less and doesn’t cause disease. Because more measles proteins are made during natural infection than after immunization, the immune response to natural infection is greater than the immune response to immunization.

If the immune response is greater after natural infection, then the autoimmune response would also be greater. If this were the case, then autoimmunity should occur more frequently after natural infection than after vaccination. Or, said another way, if measles virus caused autism, measles vaccination would lower, not raise, the incidence of autism.

The second theory is that the child’s immune system is simply overwhelmed by seeing three viruses in a vaccine at the same time. Some have gone so far as to suggest that it may be of benefit to divide the MMR vaccine into three separate vaccines. The rationale behind this theory is that children do not normally encounter such an assault on the immune system. However, this notion is incorrect.

From the birth canal and beyond, infants are confronted by a host of different challenges to their immune system. Their intestines encounter foreign proteins in milk and formula. Their lungs encounter bacteria inhaled on the surface of dust in the air. And literally thousands of different bacteria immediately start to live on the skin, as well as on the lining of the nose, throat, and intestines. So how does the infant deal with this immediate confrontation to their immune system?

Babies have a tremendous capacity to respond to their environment from the minute they are born. The newborn has billions of immunologic cells that are capable of responding to millions of different microorganisms. By quickly making an immune response to bacteria that live on the surface of their intestines, babies keep those bacteria from invading their bloodstream and causing serious disease. Therefore, the combination of the three vaccines contained in MMR, or even the 10 vaccines given in the first 2 years of life, is literally a raindrop in the ocean of what infants successfully encounter in their environment every day.  

Because the peak of some diseases (such as pertussis and Haemophilus influenza type b) occurs in early infancy, it is important to make sure that children are fully immunized against these diseases by 6 months of age. This is easily accomplished. About 95% of infants will develop protective antibodies following immunization because their immune systems are quite capable of responding to vaccines.    

The third theory is that the MMR vaccine is given by an unnatural route. The rationale behind this theory is that children normally inhale measles, mumps, or rubella viruses carried on droplets from another person, and do not normally have virus injected under the skin. However, encountering viruses or bacteria under the skin or within the muscles does occur naturally. To meet this challenge, children have collections of immune cells in lymph glands located strategically throughout the body. For example, lymph glands are located behind the elbow and under the arm. Because our skin can be cut, our bodies are ready to encounter challenges at any site. Indeed, although wondrous, the birth process is quite traumatic. Newborns commonly have small cuts on the face and body after passing through the birth canal. Because the birth canal is covered with bacteria, the child will encounter bacteria under the skin immediately. Our species survives because, from the minute we are born, we are quite capable of meeting challenges at all sites.    

To review, I have made three points that counter the plausibility that autism would be a consequence of the MMR vaccine, or, more importantly, any vaccines: First, if autism is a consequence of autoimmunity, then the incidence of autism would have decreased, not increased, after vaccination.

Second, children from birth are confronted with an enormous array of different challenges to their immune system at the same time.

Third, challenges to their immune system occur by a variety of routes.

These are medical facts.

Parents testifying here today are asking a scientific question, “Does the MMR vaccine cause autism?” Questions of science are best answered by scientific studies. And the answer to this question is already available. Brent Taylor and his coworkers in London have conducted a large, meticulously designed, well-controlled study that disproved an association between MMR vaccine and autism. I believe other studies will confirm Dr. Taylor’s results. 

We also have to ask ourselves this question, “What is really at stake here?” In the early 1990s our immunization rates against measles dropped only about 10%. When that happened, measles outbreaks swept across the country. About 11,000 people were hospitalized and 123 died from measles – died from a disease that is easily and safely prevented by a vaccine.

My concern, and it should be the concern of this committee, Mr. Chairman, is that some parents listening to or reading about this hearing might incorrectly conclude that vaccines cause autism. This is clearly not the case – vaccines are extremely safe and highly effective at preventing serious disease and death. I encourage this committee to make that fact clear to every parent in America.

If, as a result of reading about this hearing, some parents choose to withhold or delay vaccines for their children, their tragedy could be profound. If many parents choose to withhold vaccines, the tragedy all across America could be devastating.

Let’s proceed cautiously, carefully, and scientifically.

Mr. Chairman, I am ready to respond to any questions the committee might have.  

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