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In easy-to-understand language
Note: The terms "immunization," "vaccination," and "inoculation" are used to mean essentially the same thing throughout this site.
Is there any scientific evidence that proves a linkage between autism and vaccines?

To date, there is no conclusive evidence that any vaccine can cause autism.

What about the Wakefield study?

The study that initially suggested a link between the MMR vaccine and autism was published in Lancet by Wakefield and colleagues in 1998 (Wakefield et al 1998). Based on data from 12 patients who were diagnosed with bowel disease and autism, the authors of this study speculated that, based on the parents� recall, the measles/mumps/rubella (MMR) vaccine may have been a possible cause of the neurological disease and bowel problems. The researchers theorized that the bowel disease could have led to decreased absorption of essential vitamins and nutrients, which in turn could have led to developmental disorders, like autism. However, the study focused on anecdotal evidence; the authors performed no scientific analyses to substantiate their theory. An editorial published in the same issue of Lancet voiced concerns about the validity of the study (Chen and DeStefano 1998). It is difficult to determine whether the 12 reported cases represent an unusual or unique clinical syndrome without knowing the size of the patient population from which the 12 were identified and the duration of time allotted for reporting cases. Without evidence supporting or disputing a selective referral process, a referral bias that sent only the 12 cases noted in the study to the authors practice cannot be ruled out. The authors stated that additional cases have been identified; however, detailed clinical characterization of the neurological diseases and documentation of timing of vaccination, autism and bowel disease onset in all these children has not been provided.

The theory that autism might be caused by poor absorption of nutrients resulting from a bowel inflammation is also not supported by clinical data. In at least four of the 12 cases reported in the Lancet study, behavioral problems appeared before the onset of symptoms of inflammatory bowel disease; that is, the effect preceded the proposed cause. The same authors published another study in which they performed highly specific laboratory assays of patients with inflammatory bowel disease following MMR vaccination, the cause for autism they posited in their initial study. These patients tested negative for the measles virus, which would not support the theory the authors posed in their original study (Chadwick et al 1998, Duclos and Ward 1998).

Subsequently, these authors and other collaborators have reported detection of measles virus from blood cells and intestinal samples from children with autism and inflammatory bowel disease (Kawashima et al 2000). The authors also report detection of wild type and vaccine strains of measles virus RNA in patients with inflammatory bowel diseases without the diagnosis of autism, thus making it impossible to associate measles virus RNA with autistic disorders. Other scientists have published studies that measles virus RNA (Afzal MA et al 2000) and protein (Iizuka M et al 2000) are not present in intestinal specimens from patients with inflammatory bowel diseases.

Although gastrointestinal problems have been documented in a subgroup of persons with autism, studies remain inconclusive. One recent study indicated that unrecognized gastrointestinal disorders in non-verbal autistic patients may contribute to behavioral problems (Horvath et al 1999). However, authors of the study were pointed in their conclusion that additional research is required to determine any possible association between the brain and gastrointestinal dysfunction in autistic children.

Is there any independent research that supports the safety of the MMR vaccine?

Other recent investigations show no causal relationship between MMR (or other measles-containing vaccines) and either autism or inflammatory bowel disease.

In 1999, the Working Party on MMR Vaccine of the United Kingdom�s Committee on Safety of Medicine evaluated several hundred reports, collected by lawyers of patients with autism, Crohn�s disease, and similar disorders that were supposedly developed after receiving the MMR or MR vaccine. The Party acknowledged that it was impossible to prove or refute the suggested associations because of variable data quality, biased selection of cases, and lack of a control group. However, after a systematic, standardized review of parental and physician information, the Working Party concluded that the information available did not support the suggested causal associations or give cause for concern about the safety of MMR or MR vaccines.

Another study published in Lancet by Taylor and colleagues provides population-based evidence that overcomes a number of limitations that the Working Party and the Wakefield group experienced (Taylor et al 1999, DeStefano and Chen 1999). The authors identified all 498 known cases of autism spectrum disorders (ASD) in children living in certain districts of London who were born in 1979 or later and correlated the cases to an independent vaccination registry. (ASD includes classical autism, Pervasive Developmental Disorder, Not Otherwise Specified {PDD NOS} or atypical autism, and Asperger�s syndrome.) The results of this study were as follows:

  1. The authors showed that the number of ASD cases has been increasing since 1979, with no jump after the introduction of the MMR vaccine in 1988.
  2. The authors found that children who were vaccinated before 18 months of age were diagnosed with autism at ages similar to children who were vaccinated after 18 months of age, indicating that the vaccination did not result in earlier expression of ASD characteristics.
  3. The authors discovered that at age two, the MMR vaccination coverage among ASD cases was nearly identical to vaccination coverage of children in the same birth cohorts in the whole region, providing evidence of a lack of overall association between the ASD and the vaccination.
  4. Taylor and colleagues established that the first diagnosis of autism or initial signs of behavioral regression were not more likely to occur within time periods following MMR vaccination than during other time periods. However, parental concern clustered at six months post-vaccination.
  5. The results of the study were similar when cases of classical autism were analyzed separately.

In 1997, the National Childhood Encephalopathy Study (NCES) examined any possible link between measles vaccine and neurologic events (Miller et al 1997). Researchers in England found no indication that the measles vaccine contributes to the development of long-term neurological damage, including educational and behavioral deficits.

Another study also showed no evidence of association between the MMR vaccine and autism (Gillberg and Heijbel 1998). The study compared autism prevalence rates in populations of children from two communities in Sweden (prior to 1982). The results indicated no difference in autism prevalence between children born after the introduction of the MMR vaccine in Sweden and those born before the vaccine was used.

Several other published epidemiological studies show no causal association between MMR vaccination and autism or inflammatory bowel disease, including retrospective studies that showed no association between the rates of autism and vaccine coverage in young children (Dales, Hammer and Smith 2001; Kaye JA, del Mar Melero-Montes M, Jick H 2001), and prospective studies of vaccine associated adverse events (Peltola et al 1998). Other studies have reported no increased risk for inflammatory bowel disease in children vaccinated with MMR (Davis RL et al 2001; Morris DL et al 2000). Additional studies are underway (Smeeth et al 2001).

What is the Federal Government doing to protect the health of those people who receive the MMR or other measles-containing vaccines?

To ensure the safety of vaccines, the Centers for Disease Control and Prevention (CDC), the Food and Drug Administration (FDA), the National Institutes of Health (NIH), and other Federal agencies routinely monitor and conduct research to examine any new evidence that would suggest possible problems with the safety of vaccines.

The CDC has conducted research and found no epidemiological evidence for causal association between autism and MMR vaccine (DeStefano F and Chen RT 2000). Currently, the CDC is conducting a case-control study in metropolitan Atlanta, Georgia, to further evaluate any possible association between the administration of MMR vaccine and autism. This prevalence study uses the only current population-based sample of school-aged children in the United States with autism. The results of this study are expected sometime in 2001.

Similarly, the NIH is also conducting correlational studies of such an association. A retrospective study of persons diagnosed with autism who regressed after apparently normal development and matched comparison groups is underway. The National Institute of Child Health and Human Development (NICHD) and the National Institute of Deafness and Other Communication Disorders (NIDCD), two components of the NIH who fund the Network on the Neurobiology and Genetics of Autism: Collaborative Programs of Excellence in Autism (CPEA), are working together with the CDC in this endeavor. Additional funding and participation from the CDC will allow more extensive medical evaluation, as well as collection of vaccination serology and records information. The effort represents the largest study to date comparing autistic patients who have regressed with groups of autistic children who did not regress and children who developed normally.

In addition, the NICHD is working with other NIH Institutes, the CDC, the Environmental Protection Agency, and other Federal agencies to conduct a large, long-term study of the effects of the environment on children�s health. This study will follow 100,000 children from before birth to age 20, to track growth and development, as well as study genetic blueprints and environmental factors. Researchers hope to establish or rule out links between a variety of environmental events and normal and abnormal development, such as autism. This prospective study is currently under design.

Another NIH Institute, the National Institute of Neurological Disorders and Stroke (NINDS), is conducting a retrospective case-control study to identify any molecular markers in neonatal blood of children with autism, with support from California Department of Health Services and the Bioengineering and Physical Science (BEPS) Program of the NIH.

Other recent NIH-sponsored research has also led to the refinement of screening and diagnosis procedures for various autism disorders that will facilitate better estimates of the incidence and prevalence of these disorders and provide earlier identification and treatment. Overall, the thrust of the NIH research is to explore all the possible causes of autism, including those that may be associated with regression after apparently normal development.

Health care providers who administer vaccines are required to report any adverse health events that occur in persons who have received vaccines to the Vaccine Adverse Event Reporting System (VAERS), a database which is co-maintained by the CDC and the FDA. More specific information on VAERS, adverse event reporting, and the reporting process, is provided in the Vaccine Adverse Event Reporting section of this information packet.

Because there are no proven data to suggest that the MMR vaccine increases the risk of developing autism or another behavioral disorder, the CDC maintains its recommendation that children with no known health contraindication receive two doses of MMR vaccine. (&Recommendations of the Advisory Committee on Immunization Practices {MMWR 1998} identifies specific contraindications.) The first dose is recommended at age 12-to-15 months of age, while the second dose is recommended at either four-to-six years of age or 11-to-12 years of age. Contraindications to the MMR vaccine are outlined in the Recommendations of the Advisory Committee on Immunization Practices (ACIP), MMWR 1998.

Is there a theoretical possibility of a connection between autism and the MMR or any other vaccine?

Because millions of children have received the MMR and other vaccines without ill health effects, it would have to be a rare occurrence for MMR or other vaccines to cause autism.

In January 1990, an Institute of Medicine (IOM) committee examined possible health effects associated with the diphtheria/tetanus/pertussis (DTP) vaccine. The Committee concluded that there was no evidence to indicate a causal relationship between the DTP vaccine, or the pertussis component of the vaccine, and autism. Furthermore, data obtained from the CDC�s Monitoring System for Adverse Events Following Immunization (MSAEFI) showed no reports of autism occurring within 28 days of DTP immunization from 1978 to 1990. Approximately 80.1 million DTP vaccines were administered during this time period, with no documented link to a case of autism.

From January 1990 through February 1998, VAERS reported only a small number of autism behavior disorder cases that occurred following an immunization. Because the number of cases reported in this eight-year period was so small, autism researchers concluded that they likely represent unrelated events that occurred around the time of vaccination. Additional research is needed to determine whether individuals who may have a susceptibility to a vaccine, or one or more components of a vaccine, or who may need adjustments to the timing or number of vaccinations they receive can be identified. DTP, oral polio vaccine, and MMR were the vaccines most often cited in the VAERS-reported cases.

What are the known side effects of the MMR vaccine?

  • Most people who receive the MMR vaccination have no reaction to it.
  • About 5-15 percent of those receiving the MMR vaccination develop a fever after 5-12 days. Similarly, 5 percent may develop a rash after 5-12 days.
  • Central nervous system conditions, including encephalitis and encephalopathy, have been reported with a frequency of less-than 1 per 1,000,000 doses of vaccine administered.
  • As with the administration of any agent that can cause fever, the MMR vaccine may cause simple febrile seizures in some children. These convulsions affect children with no known risk factors for seizure. Children with a prior history of convulsions may be at increased risk for febrile seizures following MMR vaccination.

For more information on autism and autism research, contact the National Institute of Child Health and Human Development (NICHD) Clearinghouse at 1-800-370-2943, or visit these NIH web sites:

The CDC�s National Center on Birth Defects and Developmental Disabilities (NCBDDD) also provides information about autism on their web site at:

For more information on vaccines and vaccine safety, contact the National Immunization Program (NIP) at 800-232-2522 (English) or 1-800-232-0233 (Spanish), or visit the NIP web site at


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Afzal MA, Armitage E, Ghosh S, Williams LC, Minor PD. Further evidence of the absence of measles virus genome sequence in full thickness intestinal specimens from patients with Crohn�s disease. J Med Virol 2000; 62:377-82.

**American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. Washington, DC: American Psychiatric Association, 1994.

Bailey, A., Hervas, A., Matthews, N., et al. International Molecular Genetic Study of Autism Consortium. (1998). A full genome screen for autism with evidence for linkage to a region on chromosome 7q. Human Molecular Genetics, 7:571-578.

*Bristol MM, Cohen DJ, Costello EJ, et al. State of the science in autism: Report to the National Institutes of Health. J Autism Developmental Disorders 1996;26:121-54.

Chadwick N, Bruce IJ, Schepelmann S, Pounder RE, Wakefield AJ. Measles virus DNA is not detected in inflammatory bowel disease using hybrid capture and reverse transcriptase followed by polymerase chain reaction. J Med Virol 1998;55:305-311.

Chen RT, DeStefano F. Vaccine adverse events: causal or coincidental? Lancet 1998; 351:611 -612.

Dales L, Hammer SJ, Smith NJ. Time trends in autism and in MMR immunization coverage in California. JAMA 2001; 285:1183-5.

Davis RL, Kramarz P, Bohlke K, Benson P, Thompson RS, Mullooly J, Black S, Shinefield H, Lewis E, Ward J, Marcy SM, Eriksen E, DeStefano F, Chen R. Arch Pediatr Adolesc Med 2001; 155:354-359.

DeStefano F, Chen RT. Negative association between MMR and autism. Lancet 1999;353:1987-8.

DeStefano F, Chen RT. Autism and measles, mumps and rubella vaccine: No epidemiological evidence for a causal association. J Pediatr 2000 136:125-6.

Duclos P, Ward BJ. Measles vaccines: a review of adverse events. Drug Safety 1998;19:435-454.

Ekbom A, Wakefield AJ, Zack M, Adami HO. Perinatal measles infection and subsequent Crohn's disease. Lancet 1994;344:508-10.

**Fombonne E, Epidemiological Findings on Autism and Related Developmental Disorders. Workshop on Educational Interventions for Children with Autism. The National Academies (NAS), Washington, DC, Dec. 13-14, 1999.

Gillberg C, Coleman M. Autism and medical disorders: A review of the literature. Developmental Medicine and Child Neurology 1996;38:191-202.

Gillberg C, Heijbel H. MMR and autism. Autism 1998;2:423-4.

Horvath K, Papadimitriou JC, Rabsztyn A, Drachenberg C, Tildon JT. Gastrointestinal abnormalities in children with autistic disorders. J Pediatr 1999 Nov;135(5):559-63.

IOM, Adverse Effects of Pertussis and Rubella Vaccines, Institute of Medicine, 1991.

IOM, Adverse Events Associated with Childhood Vaccines, Evidence Bearing on Causality, 1994.

Iizuka M, Chiba M, Yukawa M, Nakagomi T, Fukushima T, Watanabe S, Nakagomi O. Immunohistochemical analysis of the distribution of measles related antigen in the intestinal mucosa in inflammatory bowel disease. Gut 2000; 46:163-9.

Kawashima H, Mori T, Kashiwagi Y, Takekuma K, Hoshika A, Wakefield A. Detection and sequencing of measles virus from peripheral mononuclear cells from patients with inflammatory bowel disease and autism. Dig Dis Sci 2000; 45:723-9.

Kaye JA, del Mar Melero-Montes M, Jick H. Mumps, measles and rubella vaccine and the incidence of autism recorded by general practitioners: a time trend analysis. BMJ 2001; 322:460-3.

Medicines Commission Agency/Committee on Safety of Medicines. The safety of MMR vaccine. Curr Probl Curr Pharmacovigilance 1999;25:9-10.

Metcalf J. Is measles infection associated with Crohn's disease? Brit Med J 1998;316:561.

Miller D, Wadsworth J, Diamond J, Ross E. Measles vaccination and neurological events. Lancet 1997;349:730-31.

MMWR, Measles prevention: recommendations of the immunization practices advisory committee, MMWR 1989;Vol.38 / No.S-9.

&MMWR, Measles, mumps, and rubella-vaccine use and strategies for elimination of measles, rubella and congenital rubella syndrome and control mumps: recommendations of the advisory committee on immunization practices. MMWR. 1998. Vol. 47. No. RR-8.

Morris DL, Montgomer SM, Thompson NP, Ebrahim S, Pounder Re, Wakefield AJ. Measles vaccination and inflammatory bowel disease: a national British cohort study. Am J Gastroenterol 2000; 95:3507-12.

Peltola H, Patja A, Leinikki P, Valle M, Davidkin I, Paunio M. No evidence for measles, mumps and rubella vaccine-associated inflammatory bowel disease or autism in a 14-year prospective study. Lancet 1998; 351:1327-8.

Piven J, The Biological Basis of Autism, Current Opinion in Neurobiology, 1997, 7: 708-12.

Rodier PM, Hyman SL. Early environmental factors in autism. MRDD Research Reviews 1998;4:121-128.

Smeeth L, Hall AJ, Fombonne E, Rodriques LC, Huang X, Smith PG. A case-control study of autism and mumps-measles-rubella vaccination using the general practice research database: design and methodology. BMC Public Health 2001; 1:2.

Taylor B, Miller E, Farrington CP, et al. Autism and measles, mumps, and rubella vaccine: no epidemiological evidence for a causal association. Lancet 1999;353:2026-9.

Wakefield AJ, Murch S, Anthony A, et al. Ileal lymphoid nodular hyperplasia, non-specific colitis, and regressive developmental disorder in children. Lancet 1998;351:637-41.

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Last updated: August 2001

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