MMR Vaccine and Autism : Part 3

by CDC

(Page 4 of 5)

In another study that generated media attention and raised public concern in the UK (Uhlmann et al, 2002), researchers found measles virus fragments in the intestines of children with "new variant" IBD (children with both IBD and developmental disorder). Scientists looked for the presence of measles virus in the intestinal tissue of 91 children with new variant IBD and 70 "controls" (children without this type of IBD). The researchers found measles virus fragments in 75 out of the 91 children with "new variant" IBD, and in only 5 of the 70 controls. While this provides evidence for an association between the presence of measles virus and IBD in children with developmental disorder, it does not mean that the measles component of the MMR vaccine causes IBD or developmental disorder. As a commentary published with the article asserts, the data could just as easily be interpreted as indicating that the IBD or the developmental disorder cause the persistence of measles in the intestines (Morris & Aldulaimi, 2002). In addition, the researchers did not compare the virus found in the intestines of patients with the virus used in the MMR vaccine; nor did they provide information regarding whether or not the children in the study had been previously vaccinated with MMR or had previously contracted measles disease. The limitations of this study are further discussed in a letter written by the Director of CDC's National Immunization Program to the UK's Chief Medical Officer.

What about the claim that the number of children with autism has been increasing ever since the MMR vaccine has been in use?

Data from California (Department. of Developmental Services, 1999) have been used to illustrate an increase in cases of autism since the introduction of MMR vaccine. However, the data have been presented inaccurately (Fombonne, 2001). Fombonne (2001) lists several reasons why the data are misrepresented, for instance:

1. the figures presented are based on numbers, not rates and do not account for population growth and changes in the composition of the population,

2. changes in diagnostic definitions were not controlled in the report, and

3. as in other areas of the country, children with autism are currently being diagnosed at earlier ages meaning that there will be an increase in the number of reported cases.

A 2001 study (Dales et al.) used the autism case numbers provided by the California Department of Developmental Services and compared them with early childhood MMR immunization level estimates for California children. Results showed that for children born from 1980 through 1987, there was no major change in MMR immunization levels with the exception of a small increase in children born in 1988. This small increase was followed again by steady levels in children born through 1994. On the other hand, the cases of autism increased markedly, from 44 cases per 100,000 live births in 1980 to 208 cases per 100,000 live births in 1994. Even if one allows that a true increase in autism has occurred and the increase is not due to changes in diagnostic methods, diagnostic categorization, and improved identification of individuals with autism because of the level of services offered (Fombonne, 2001), this analysis shows that receipt of the MMR vaccine is not a factor. If it were a factor, one would expect the shape of the MMR level of immunization curve to be very similar to the autism case numbers. This is not the case, thus the analysis in this study argues against a link between MMR vaccination and autism.

Would it be safer to separate the MMR vaccine into its individual components--in other words, give children three separate shots, at different times (e.g., six months or one year apart), instead of one combined shot?

There is no confirmed scientific research or data to indicate that there is any benefit to separating the MMR vaccine into its individual components. A publication by Wakefield and Montgomery (2001) suggests that there is an increased risk of immune-mediated disease when the MMR vaccine is administered as one vaccine versus when the 3 vaccines are administered separately. The specific issue of the safety of multiple vaccines given as one vaccine was addressed by the Institute of Medicine (IOM) (1994, p.63). They stated that the number of separate antigens in a vaccine would not likely result in a significant burden on the immune system that would result in immunosuppression. The issue of multiple vaccines and immune dysfunction was addressed again by the IOM in 2002. An IOM Immunization Safety Review Committee concluded that a review of the available scientific evidence does not support the suggestion that the infant immune system is inherently incapable of handling the number of antigens that children are exposed to during routine immunizations. The IOM committee also did not suggest any need to change the current US vaccination schedule for MMR.

Splitting the MMR vaccine into three separate doses given at three different times would cause more discomfort from additional injections and would leave children exposed to potentially serious diseases. For instance, if rubella vaccine were delayed, 4 million children would be susceptible to rubella for an additional 6 to 12 months. This would potentially allow otherwise preventable cases of congenital rubella syndrome (CRS) to occur through transmission of rubella from infected children to pregnant women. Ironically, infection of pregnant woman with "wild" rubella virus is one of the few known causes of autism. Thus, by preventing rubella infection of pregnant women, MMR vaccine also prevents autism.

About the Author

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The Centers for Disease Control and Prevention (CDC) is one of the 13 major operating components of the Department of Health and Human Services (HHS), which is the principal agency in the United States government for protecting the health and safety of all Americans and for providing essential human services, especially for those people who are least able to help themselves.