© Borgis - Postępy Nauk Medycznych 5/2010, s. 422-428
*Monika Suchowierska1, Gary Novak2
Measles-mumps-rubella vaccine and autistic spectrum disorder: What do doctors need to tell the parents?
Potrójna szczepionka przeciwko odrze, śwince i różyczce a spektrum zaburzeń autystycznych: o czym lekarze powinni informować rodziców?
1Warsaw School of Social Sciences and Humanities, Department of Psychology (Fulbright Scholar at CSU Stanislaus)
Head of Department: dr hab. Jerzy Karyłowski, prof. SWPS
2California State University Stanislaus, Department of Psychology
Head of Department: Dr. William Potter
Autyzm jest skomplikowanym zaburzeniem rozwoju o wieloelementowej i jeszcze niecałkowicie poznanej etiologii. Cechy autystyczne są charakterystyczne dla trzech zaburzeń, często określanych w literaturze klinicznej jako „spektrum zaburzeń autystycznych” (ASD). Jedną z rzekomych przyczyn ASD jest potrójna szczepionka przeciwko odrze, śwince i różyczce (MMR). Kwestia związku pomiędzy szczepionką MMR a spektrum zaburzeń autystycznych wzbudza duże zainteresowanie wśród mediów i opinii publicznej. W 1998 r. Wakefield i współpracownicy zaproponowali hipotezę dotyczącą związku szczepionki MMR i ASD. W ciągu ostatnich 12 lat kilkanaście badań naukowych i meta-analiz pokazało, że hipoteza Wakefielda jest nieprawidłowa. Mimo tych informacji oraz faktu, iż brak szczepień może skutkować poważnymi chorobami wieku dziecięcego, wiele osób, a zwłaszcza rodziców dzieci z autyzmem, uważa, że szczepionka MMR jest powodem ASD, w związku z czym osoby te kwestionują zasadność szczepień. Pediatrzy i lekarze rodzinni powinni informować rodziców o braku związku przyczynowo-skutkowego pomiędzy szczepionką MMR a ASD, tak aby zapobiec brakom szczepień niektórych dzieci.
Autism is a complex developmental disorder of multifaceted and not yet fully understood etiology. Autistic characteristics occur along a spectrum of three disorders, commonly referred to in clinical literature as autistic spectrum disorder (ASD). One of the purported causes of ASD that has received much public and political attention is measles-mumps-rubella vaccination (MMR). In 1998 Wakefield et al. published a study in which the authors proposed a hypothesis on the link between MMR and autism. Since then multiple experiments and meta-analyses have shown this hypothesis to be wrong. Despite the fact that the research evidence does not point to a causal link between MMR vaccination and ASD, and despite the serious medical problems associated with failure to vaccinate against these childhood diseases, there are many individuals, mainly parents of children with autism, who have arrived at conclusions based largely on personal experience pointing to MMR as the cause of their child's disorder. Pediatricians and family doctors are encouraged to educate parents about lack of connection between MMR and autism, so that parents do not refuse to vaccinate their children.
Autism is a pervasive developmental disorder that is behaviorally defined and is characterized by impairments in three areas: social interactions, reciprocal verbal and nonverbal communication and the range of interests and activities (1). The current definition of autism has been refined and broadened as compared to the original description of Kanner's from 1943 (2). Nowadays, persons with autism are considered to present with neurodevelopmental abnormalities that have such wide range of behavioral symptoms and severity that they are collectively referred to as pervasive developmental disorders (PDDs) in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders, Text Revised (1). Within the group of five pervasive developmental disorders, a narrower term of autism spectrum disorders (ASDs) is used to refer to: autistic disorder, Asperger's disorder and pervasive developmental disorder – not otherwise specified. In this article we will use the term "autism” and "autistic” broadly to refer to the whole range of ASDs.
Since Kanner's 1943 classic paper (2) describing a pattern of behavior that he referred to as "early infantile autism” and through the 1990s, autism had been thought of as a rare condition (3). It is not the case nowadays. Scientists and journalists refer to "an epidemic of autism” (4). Autism is said to be more prevalent than spina bifida, cancer, or Down syndrome (5). Fombonne (6) writes that available data places "PDDs, particularly autistic disorder, among the most prevalent medical conditions of childhood” (p. 7). Research on the incidence/prevalence of this disorder is important for a better understanding of its etiology, assessment and services available for individuals with autism. Knowledge of the incidence (i.e., the number of new cases occurring over time) would be more informational about the alleged "epidemic”, but incidence studies would require identification of a definite time of onset in a defined population at risk. This is a difficult task because the wide range of behaviors necessary for a diagnosis of autism may not be apparent in all children at a specific age. Thus, most of the studies determine prevalence (i.e., the extent of a problem across a population at a particular point in time) rates.
The first three epidemiological studies report prevalence of autism in the range of 0.7 to 4.5 per 10 000 children (7, 8, 9). However, over time there has been a marked increase in those rates (10, 11). The US Department of Education reported an astonishing 556% rise in prevalence of autism between 1991 and 1997 (12). Several review studies indicate that the current rate for PDD is between 30 and 60 cases per 10 000 children, with a quarter of those meeting the full criteria for autism (13). According to Fombonne (11), the best estimate for the prevalence rate of autistic disorder is 10 per 10 000. The Centers for Disease Control reported in 2007 an estimated prevalence rate for ASDs 1 case in 150 children, and in 2009 – 1 case in 110 children (14, 15). Despite the fact that most of the information comes from the United Kingdom and the United States, epidemiological data have been gathered from 14 countries (6) and increases are reported worldwide (16).
Wing and Potter (3) list several potential reasons for this marked rise in prevalence: 1) changes in the diagnostic criteria, 2) varied methodology of epidemiological studies, 3) increased professional and public awareness of autism, 4) expansion in therapeutic and educational services, and 5) genuine rise in incidence of ASDs. For the purposes of the present paper, we will elaborate on the last assumption. If there were a true increase in incidence of ASDs it could be attributable to some environmental hazard (13). Many suggestions have been made considering the influence of environmental factors on autism: prenatal exposure to chemical agents such as thalidomide and valproic acid, as well as to infectious agents such as the rubella and influenza viruses, postnatal influences of diets, environmental pollutants, antibiotics, vaccinations, and neurotoxins such as mercury present in preservatives used for some vaccines (3, 17, 18, 19). None of those, however, has been yet scientifically validated. The purported link between measles-mumps-rubella (MMR) vaccine and ASDs has received much public and political attention (20, 21, 22) and will be the focus of the remainder of the article. Information presented below is a summary of several review articles and reports (23, 24, 25, 26, 27, 28, 29, 30, 31).
The hypothesis relating MMR immunization and the onset of symptoms of ASD was advanced by Andrew Wakefield and his colleagues in an 1998 article (32) describing 12 children with inflammatory bowel conditions and developmental disorders, primarily autism. For 8 out of the 12 children either the parent or the physician associated the MMR vaccination with the onset of behavioral problems and regression in the child's functioning. The average latency between the receipt of the injection and the occurrence of the symptoms was 6 days. Additionally, 9 children were diagnosed with lymphoid nodular hyperplasia in the terminal ileum as determined by endoscopy. A hypothesis was put forth that there is a new variant of ASD (regressive autism characterized by gastrointestinal symptoms) that originates from the MMR vaccine. The authors proposed the following sequence of events: 1) MMR produces inflammation in the intestines, 2) inflammation in the gut results in the change in intestinal barrier function that allows for the passage of toxic neuropeptides, 3) peptides disregulate the endogenous opioid system and subsequently cause central nervous system damage, which in turn results in developmental regression. This hypothesis has been called "gut-mediated toxic encephalopathy hypothesis” or "Wakefield hypothesis” (27). Despite the fact that Wakefield's study was heavily criticized on methodological grounds (i.e., small number of cases, no unaffected comparison group, possibility of a coincidental, not causal, temporal relation between the MMR vaccine and autism), the fact that subsequent studies by the same group of researchers did not support the original hypothesis (33) and the fact that in 2004 10 of the 13 authors of the 1998 paper asked to "formally retract the interpretation placed upon these findings” (34), the original publication raised great interest and public attention with regards to safety of the MMR vaccine. The result was a drop in the number of children immunized. In England, for example, MMR immunization rates dropped from greater than 90% prior to 1998 to a low of 75% in 2003-2004 (28) and cases of measles increased from 56 cases in 1998 to 1.370 cases in 2008 (35). Suspicions about the MMR vaccine spread to the USA. Many parents refuse or delay administration of the vaccination and ask the physicians to use three separate vaccines instead of the three-in-one shot. Needless to say, Wakefield's article had a far-reaching impact that had to be mitigated by epidemiological studies investigating in-depth the purported link between MMR and autism.
There are at least 20 epidemiological studies related to MMR and ASDs that have been published since the 1998 Wakefield's article. Sixteen of them were closely scrutinized and evaluated in the Immunization Safety Review. Out of the 16, nine are controlled observational studies (36, 37, 38, 39, 40, 41, 42, 43, 44), four are ecological studies (45, 46, 47, 48), and three are studies based on passive reporting system (49, 50, 51). Five other studies (52, 53, 54, 55, 56) were not included in the ISR review, but are discussed in other reviews. The 20 studies were conducted in six different countries (the United States, the United Kingdom, Finland, Denmark, Sweden, and Japan), used at least 12 distinct data sources, and employed a variety of study designs, including time-series analysis, cross-sectional analysis, ecologic analysis, case control, and retrospective cohort. The majority of studies were designed to address specific hypotheses that stemmed from Wakefield's study. These hypotheses are:1) ASD rates are higher among children who have received the MMR vaccine as opposed to those who have not, 2) increased rates of ASD occur as a consequence of the MMR vaccine, 3) the onset of ASD is temporally associated with receipt of the MMR vaccine, and 4) there is a new variant of ASD related to the MMR vaccine (31).
Only one study examined Hypothesis 1 (40). Danish researchers conducted a retrospective cohort study of all children born in Denmark between January 1991 and December 1998. A total of 537 303 children were included in the cohort, 440 655 (82%) of whom were vaccinated with the MMR vaccination. The researchers analyzed the relative risk of autistic disorder and other ASDs in vaccinated and unvaccinated children. Analysis was adjusted for age, calendar period, sex, birth weight, gestational age, mother's education, and socioeconomic status of the family. The results showed no statistically significant differences in rates of autism and ASDs in those two populations. Additionally, there was no relation between the age at the time of vaccination, the time since vaccination, or the date of vaccination and the development of ASD. The authors concluded that their "study provides three strong arguments against a causal relation between MMR vaccination and autism” (p. 1480): 1) the risk of autism was similar in vaccinated and unvaccinated children, 2) there was no temporal clustering of cases of autism at any time after immunization, 3) neither autism nor other ASDs were associated with the MMR vaccination.
Six studies examined Hypothesis 2 (39, 43, 44, 45, 47, 48).
Dales et al. (45) investigated whether there is correspondence between the trends in MMR coverage and numbers of ASD cases. The authors conducted a retrospective analysis of MMR immunization rates among children born between 1980 and 1994 who were enrolled in California kindergartens and cases of children born in these years who were diagnosed with autism and were enrolled in the California Developmental Services system. The results show essentially no correlation between those two variables. Between the years 1980 and 1994, the increase in the coverage of the MMR vaccination was 14% and the increase was observed for the cohort born in 1988 – before that year and after that year the data were stable. As for the autism caseloads, there was a steeply increasing trend (a relative increase of 572%) beginning in 1985 and continuing to 1994. The authors concluded that their results "do not support the hypothesis that increasingly widespread MMR immunization of young children is associated with the marked secular trend of increasing number of autism cases” (p. 1185).
Fombonne and Chakrabarti (39) conducted a cross-sectional study to examine whether a new variant of autism, characterized by regression and bowel symptoms, is associated with MMR. The authors stated that if there were a new phenotype of autism, at least one of the following six predictions would have to be supported by empirical data: "1) childhood disintegrative disorder (CDD) has become more frequent, 2) the mean age of first parental concern for autistic children who are exposed to MMR is closer to the mean immunization age than in children who are not exposed to MMR, 3) regression in the development of children with autism has become more common in MMR-vaccinated children, 4) the age of onset for autistic children with regression clusters around the MMR immunization date and is different from that of autistic children without regression, 5) children with regressive autism have distinct symptom and severity profiles, and 6) regressive autism is associated with gastrointestinal symptoms and/or inflammatory bowel disorder” (p. 1). Three samples of children were used: the main sample (96 children born between 1992 and 1995 with a pervasive developmental disorder diagnosis, 99% received the MMR vaccine thus called a "post-MMR sample”) and two comparison samples (comparison sample 1 – 68 children born between 1987 and 1996 with a diagnosis of PDD, most of these children were likely to have been exposed to the MMR vaccination, thus called "post-MMR sample”); comparison sample 2 – 99 individuals born between 1954 and 1979 with a diagnosis of autism, none of them received the MMR vaccine, thus called "pre-MMR sample”). The experimenters tested the six hypotheses mentioned above and obtained the following results: 1) there was no evidence that CDD rate was increased among children who were exposed to MMR immunization, 2) there was no difference across the pre-MMR sample and the two post-MMR samples in the mean age at which parents became concerned about autistic symptoms of their child, 3) there was no evidence that regressive autism has increased in frequency, 4) when compared with parents of autistic children without regression, parents of children with regressive autism did not become concerned at an earlier age or at an age closer to the MMR immunization date, 5) no statistically significant difference was found between the group of children with regression and the group without regression, suggesting a great similarity for patterns and levels of autistic symptomatology, and 6) no association was found between gastrointestinal symptoms and regression. The authors concluded that there is "lack of evidence for a new phenotype of MMR-induced autism” (p. 7).
Gillberg and Heijbel (47) compared via a case series analysis proportions of autistic cases in high and low MMR coverage periods. The authors reanalyzed data obtained from a population study of autism performed in the late 1980s. Seventy four children (55 with the diagnosis of autistic disorder and 19 with the diagnosis of atypical autism) were divided into two groups based on era of birth, as a proxy for exposure to the MMR vaccine. The MMR vaccine was introduced for 18-month-old children in Sweden in 1982, so the pre-MMR group consisted of children born between January 1, 1975 and June 30, 1980 and the post-MMR group consisted of children born between July 1, 1980 and December 31, 1984. The authors hypothesized that the post-MMR group would be at higher risk of developing autism if there were a correlation between MMR vaccine and autism. The prediction was not correct, as the analysis showed that 47 children with diagnosed autism or atypical autism were born in the earlier period and 27 children in the later period. Thus, the authors concluded that there is not an association between MMR vaccine and autism.
Kaye at al. (48) investigated in a time series analysis the relation between increasing rates of ASD and changes in rates of the MMR vaccine coverage in the UK. The authors obtained from the general practice research data base information about 305 cases of autism among children aged 12-years or younger, who were diagnosed in the years 1988-1999. The MMR vaccine was introduced in the UK in 1988. The estimated annual incidence of diagnosed autism had increased sevenfold from 0,3 per 10 000 person-years in 1988 to 2,1 per 10 000 person-years in 1999. Further analyses were conducted for 114 boys born between 1988 and 1993 and diagnosed between 1990 and 1999 in an attempt to assess more precisely the possibility of a temporal association between MMR vaccine and autism. The four year risk of diagnosed autism increased nearly fourfold, from 8 per 10 000 for boys born in 1988 to 29 per 10 000 for boys born in 1993. In contrast, the rates of MMR vaccination were stable (about 97%) for each successive annual birth cohort. The authors explain that if the MMR vaccine had played a role in developing autism, the risk of autism in successive birth cohorts would be expected to stop increasing within a few years from when the vaccine began in full use. The results speak to the contrary. Thus, the authors concluded that their study provides "evidence against a causal relation between MMR vaccination and the risk of autism” (p. 462).
Taylor et al. (43) compared in a time series analysis trends in the incidence of ASD before and after the introduction of the MMR vaccine in the UK. The authors identified 498 cases of ASD among children born between 1979 and mid 1998 in eight health districts in the UK. Data on the vaccination histories of those children were also obtained. The analyses revealed that: 1) there was a steady increase in cases of autism by year of birth with no sudden change in the trend line after the introduction of MMR vaccination in 1988, 2) there was no difference in age at diagnosis between the cases vaccinated before or after 18 months of age and those never vaccinated, 3) there was no temporal association between onset of autism within 1 or 2 years after vaccination with MMR, and 4) developmental regression was not clustered in the months after vaccination. The authors conclude that "our results do not support the hypothesis that MMR vaccination is causally related to autism, either its initiation or to the onset of regression” (p. 2029).
Taylor et al. (44) conducted a time series analysis to investigate whether the MMR vaccination is related to bowel problems and developmental regression in children with autism. This work was an elaboration on the 1999 study done by the same group of researchers. Taylor et al. used 5 health districts in north east London. The authors identified via computerized registers of children with disabilities, children born between 1979 and 1998 and diagnosed with autistic disorder or atypical autism. 473 children were enrolled in the study. Information on their vaccination histories, bowel problems and regression was gathered. The authors investigated in detail the relation between exposure to MMR vaccine in relation to onset of autism and the presence of bowel symptoms or regression, with adjustment for potential confounding factors – sex, year of birth, district, age at parental concern, and type of autism. The analysis confirmed no association between MMR vaccination and regression of bowel syndromes. However, the authors found out that bowel problems were reported more often for children with regression than for those without it, which may reflect particular dietary problems leading to constipation in some children with autism who have regression. The authors concluded that the results of their study failed "to support a "new variant” form of autism, where MMR vaccination is associated with developmental regression and bowel problems” (p. 394).
Eight studies examined Hypothesis 3 (temporal association between developing ASD and having received the MMR vaccine) (37, 38, 39, 40, 41, 43, 44, 50). Four of those studies have been described above.
DeWilde et al. (37) conducted a case-control study in which they compared changes in the number of consultations with the general practitioner (GP) for children who were diagnosed as autistic as compared to non-diagnosed controls, before and after the MMR diagnosis. A general practice database was used to examine whether children who were subsequently diagnosed with autism had more frequent consultations following MMR vaccine than children who were not vaccinated. There were 71 cases of children diagnosed with autism identified between 1989 and 2000 using the data base. For those children, 284 controls were chosen matched for age, sex, month of MMR vaccination, and GP practice. No significant difference in numbers of consultations in the six months and two months before and after MMR between cases and controls was identified. The authors concluded that "MMR vaccination does not appear to cause any dramatic decline in the behavior of children who subsequently become autistic” (p. 227) as indicated by no difference in the consulting behavior of the parents of the children.
Farrington et al. (38) extended the Taylor et al. (43) study, by conducting a self-matched case series method to test the hypothesis that the MMR vaccine may cause autism, without pre-specifying any fixed time interval after vaccination in which the risk for developing autism may be heightened. The researchers used the same group of children as Taylor et al. (43). Their results indicate that there was no increased incidence of diagnosis of ASD, developmental regression or parental concern relating to the child's level of functioning 24, 36 or 60 months after vaccination. There was also no increased likelihood of ASD, regression, or parental concern after vaccination compared with before vaccination. The authors concluded that their results combined with the results of Taylor et al. (43) "provide powerful evidence against the hypothesis that MMR vaccine, or indeed any measles-containing vaccine, causes autism at any time after vaccination” (p. 3635).
Makela et al. (41) conducted a retrospective cohort study in which linkage between individual MMR vaccination and the hospital discharge register was investigated. The researchers identified 535 544 1- to 7-year-old children who were vaccinated in Finland between November 1982 and June 1986. Out of those children, 352 were hospitalized for autistic disorder. 309 children were hospitalized for autism after they had received vaccination. However, no distinguishable clustering was detected in the intervals from vaccination to hospitalization (the intervals ranged from 3 days to 12 years and 5 months). The number of hospitalizations remained stable during the first 3 years after vaccination followed by a decrease, which may be expected as the child becomes older. For the children with autism who were hospitalized, none was admitted due to inflammatory bowel diseases in 1982-1995. The authors concluded that their study found "no evidence for the hypothesized link between MMR vaccination, autism, and inflammatory bowel disease” (p. 961).
Using a case-series analysis, Patja et al. (50) identified and scrutinized reports of vaccine-related complications in Norway between 1982 and 1996. The MMR vaccination was initiated in Norway in 1982, the coverage was approximately 95% and by 1996, about 1,8 million individuals were immunized. With the introduction of the MMR vaccination, a country-wide surveillance system was also put in place to detect serious adverse events associated with MMR. Patja and colleagues reviewed 173 serious adverse events that were identified by the surveillance system. During the 14 years of MMR vaccination surveillance, no cases of ASD were reported. The study provides evidence for lack of association between the MMR vaccine and ASD.
Finally, Hypothesis 4 (a new variant of ASD is related to the MMR vaccine) was investigated in four studies (39, 41, 44, 51). Three of those studies were described above.
In the fourth, Peltola et al. (51) relied on the same data base as Patja et al. (50). The researchers followed up on the 31 surveillance system reports in which children developed gastrointestinal symptoms that lasted longer than 24 hours. All children except one developed the problems after the first dose of the vaccination. The time from MMR vaccine to onset of symptoms varied from 20 h to 15 days. None of the children developed ASD. The authors concluded that their found "no data supporting the hypothesis that it (MMR vaccination) would cause pervasive developmental disorder or inflammatory bowel disease” (p. 1328).
Taken together, the available studies find "no evidence of the emergence of an epidemic of ASD related to the MMR vaccine” (31, p. 633), do "not support the hypothesis that MMR vaccine causes autism or associated disorders” (25, p. 17), provide "no evidence that MMR vaccine causes autism” (29, p. 4), and find "no convincing scientific evidence to support a causal relationship between the MMR vaccine and the development of autism” (27, p. 837). Moreover, the Immunization Safety Review: Vaccines and Autism report (26) states that "based on this body of evidence, the committee concludes that the evidence favors rejection of a causal relationship between MMR vaccine and autism” (p. 126). Despite such clear information and the efforts of national public health agencies, many parents of children with autism as well as parents of young children who are afraid that their child may develop autism have not been reassured. Why should this fear continue in the face of overwhelming scientific evidence? One prominent reason is that parents, upon receiving the devastating news that their child is autistic are frequently desperate for a cause and a cure, and to that, at this point, science does not have a straightforward answer for them. In searching for answers, parents may be offered pseudo-scientific explanations, encouraged by other parents in support groups or online. It is particularly troublesome for public health agencies when, rather than supporting the scientific data, groups attribute the data to a conspiracy on the part of governments and big pharmaceutical companies to cover up the truth. Thus, a formidable task lies ahead of doctors (especially family doctors and pediatricians) to make the results of the scientific studies compelling, understandable, and convincing for the parents who are concerned about the safely of the MMR vaccine.
What should the doctors tell the parents, then? We believe that the doctors should: 1) address the changing prevalence of the ASD in many countries of the world since mid 1980s and explain to the parents that the raising numbers are not due to a genuine change in incidence, 2) discuss the two main reasons for increases in prevalence – changes in the diagnostic criteria and greater awareness of ASD among parents and professionals, 3) talk to the parents about Wakefield's study and the difference between causal and coincidental association, 4) explain to the parents findings of the research studies conducted to test the hypothesis of a link between the MMR vaccine and autism, 5) talk to the parents about the consequences of delaying or not vaccinating their child, 6) advocate for the MMR vaccination, and 7) give parents guidance related to sources of science-based information on autism so that parents can educate themselves (e.g., Association for Science in Autism Treatment). We also believe that doctors, parents, scientists and journalists should bear in mind Bertrand Russell's words "Popular induction depends upon the emotional interest of the instances, not on their number” (57, p. 159). This quote is particularly pertinent when dealing with autism as this is still a poorly understood disorder, where new, singular unsupported information may result in very emotional reactions on the part of the parents and the media, as happened in the case of Wakefield's study. Such instances can have a long lasting, negative effect even though they have been refuted by scientific investigations. Thus, even nowadays, doctors need to tell the parents: there is no evidence that the MMR vaccine causes autism!
1. American Psychiatric Association: Diagnostic and statistical manual of mental disorders, text revised. 2000 (4th ed); Washington, DC.
2. Kanner L: Autistic disturbances of affective contact. Nervous child 1943; 2: 217-250.
3. Wing L, Potter D: The epidemiology of autistic spectrum disorders: is the prevalence rising? Mental Ret Dev Disabil Res Rev 2002; 8: 151-161.
4. California Department of Developmental Services: Autistic Spectrum Disorders. Changes in the California Caseload. An Update: 1999 through 2002. California Health and Human Services Agency 2003; Sacramento, CA.
5. Muhle R, Trentacoste SV, Rapin I: The Genetics of Autism. Pediatrics 2004; 113: 472-486.
6. Fombonne E: Epidemiology of autistic disorder and other pervasive developmental disorders. J Clin Psychiatry 2005; 66: 3-8.
7. Lotter V: Epidemiology of autistic conditions in young children, pt 1: prevalence. Soc Psychiatry 1966; 1: 124-137.
8. Brask BH: A prevalence investigation of childhood psychoses. [In:] Nordic symposium on the comprehensive care of psychotic children. Barnepsykiatrist Forening, Oslo 1972; 145-153.
9. Treffert DA: Epidemiology of infantile autism. Arch Gen Psychiatry 1970; 22: 431-438.
10. Fombonne E: Epidemiologic surveys of autism: a review. Psychol Med 1999; 29: 769-786.
11. Fombonne E: Epidemiological surveys of autism and other pervasive developmental disorders: an update. J Autism Dev Disord 2003; 33: 365-382.
12. Stokstad E: Development. New hints into the biological basis of autism. Science 2001; 294: 34-37.
13. Rutter M: Incidence of autism spectrum disorders: Changes over time and their meaning. Acta Pediatrica 2005; 94: 2-15.
14. CDC. Prevalence of autism spectrum disorders – Autism and Developmental Disabilities Monitoring Network, 14 sites, United States, 2002. Surveillance Summaries MMWR 2007; 56: 12-28.
15. CDC. Prevalence of autism spectrum disorders – Autism and Developmental Disabilities Monitoring Network, 14 sites, United States, 2006. Surveillance Summaries MMWR 2009; 58: 1-20.
16. Tidmarsh L, Volkmar FR: Diagnosis and epidemiology of autism spectrum disorders. Can J Psychiatry 2003; 48 (8): 517-525.
17. Berney TD: Autism – an evolving concept. British Journal of Psychiatry 2000; 176: 20-25.
18. Daniels JL: Autism and the environment. Environmental Health Perspectives 2006; 114: 396.
19. Szpir M: Tracing the origins of autism. A spectrum of new studies. Environmental Health Perspectives 2006; 114: 412-418.
20. Colgrove J, Bayer R: Could it happen here? Vaccine risk controversies and the specter of derailment. Health Affairs 2005; 24: 729-739.
21. O'Dell L, Brownlow C: Media reports of links between MMR and autism: a discourse analysis. British Journal of Learning Disabilities 2005; 33: (4), 194-199.
22. Speers T, Lewis J: Journalists and jabs: Media coverage of the MMR vaccine. Commun Med 2004; 1 (2): 171-181.
23. DeStefano F: MMR vaccine and autism: a review of the evidence for a causal association. Mol Psychiatry 2002; 7 (Suppl. 2): 51-52.
24. DeStefano F, Chen RT: Autism and measles-mumps-rubella vaccination: controversy laid to rest? CNS Drugs 2001; 15 (11): 831-837.
25. Halsey NA, Hyman SL: Measles-mumps-rubella vaccine and autistic spectrum disorder: report from the New Challenges in Childhood Immunizations Conference convened in Oak Brook; 2000 Jun 12-13, Illinois. Pediatrics 2001; 107 (5): 84.
26. Immunization Safety Review: Vaccines and Autism. 2004; http://www.nap.edu/catalog/10997.html
27. Madsen KM, Vestergaard M: MMR vaccination and autism. What is the evidence for causal association? Drug Safety 2004; 27: 831-840.
28. Miller L, Reynolds J: Autism and vaccination – the current evidence. Journal for Specialists in Pediatric Nursing 2009; 14: 166-172.
29. Offit PA, Coffin SE: Communicating science to the public: MMR vaccine and autism. Vaccine 2003; 22: 1-6.
30. Taylor B: Vaccines and the changing epidemiology of autism. Child: care, health and development 2006; 32: 5, 511-519.
31. Wilson K, Mills E, Ross C et al.: Association of Autistic Spectrum Disorder and the Measles, Mumps, and Rubella Vaccine. Arch Pediatr Adolesc Med 2003; 157: 428-434.
32. Wakefield AJ, Murch SH, Anthony A et al.: Ileal-lymphoidnodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children. Lancet 1998; 351 (9103): 637-641.
33. Kawashima H, Mori T, Kashiwagi Y et al.: Detection and sequencing of measles virus from peripheral mononuclear cells from patients with inflammatory bowel disease and autism. Digestive Diseases & Sciences 2000; 45 (4): 723-729.
34. Murch SH, Anthony A, Casson DH et al.: Retraction of an interpretation. Lancet 2004; 363: 750.
35. Health Protection Agency 2008: Confirmed cases of measles, mumps and rubella 1996-2008. Retrieved from: http://www.hpa.org.uk/web/HPAweb&HPAwebStandard/HPAweb_C/1195733833790
36. DeStefano F, Bhasin TK, Thompson WW et al.: Age at first measles-mumps-rubella vaccination in children with autism and school-matched control subjects: a population-based study in metropolitan Atlanta. Pediatrics 2004; 113 (2): 259-266.
37. DeWilde S, Carey IM, Richards N et al.: Do children who become autistic consult more often after MMR vaccination? British J General Practice 2001; 51 (464): 226-227.
38. Farrington CP, Miller E, Taylor B: MMR and autism: further evidence against a causal association. Vaccine 2001; 19 (27): 3632-3635.
39. Fombonne E, Chakrabarti S: No evidence for a new variant of measles-mumps-rubella-induced autism. Pediatrics 2001; 108 (4): E58.
40. Madsen KM, Hviid A, Vestergaard M et al.: A population-based study of measles, mumps, and rubella vaccination and autism. N Engl J Med 2002; 347 (19): 1477-1482.
41. Makela A, Nuorti JP, Peltola H: Neurologic disorders after measles-mumps-rubella vaccination. Pediatrics 2002; 110 (5): 957-963.
42. Takahashi H, Suzumura S, Shirakizawa F et al.: An epidemiological study on Japanese autism concerning routine childhood immunization history. Jpn J Infect Dis 2003; 56 (3): 114-117.
43. 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 (9169): 2026-2029.
44. Taylor B, Miller E, Lingam R et al.: Measles, mumps, and rubella vaccination and bowel problems or developmental regression in children with autism: population study. British Med J 2002; 324 (7334): 393-396.
45. Dales L, Hammer SJ, Smith N: Time trends in autism and in MMR immunization coverage in California. JAMA 2001; 285 (9): 1183-1185.
46. Geier DA, Geier MR: A comparative evaluation of the effects of MMR immunization and mercury doses from thimerosal-containing childhood vaccines on the population prevalence of autism. Med Sci Monit 2004; 10 (3): I33-139.
47. Gillberg C, Heijbel H: MMR and autism. Autism 1998; 2: 423-424.
48. 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. British Med J 2001; 322 (7284): 460-463.
49. Geier M, Geier D: Pediatric MMR vaccination safety. International Pediatrics 2003; 18 (2): 203-208.
50. Patja A, Davidkin I, Kurki T et al.: Serious adverse events after measles-mumps-rubella vaccination during a fourteen-year prospective follow-up. Pediatr Infect Dis J 2000; 19 (12): 1127-1134.
51. Peltola H, Patja A, Leinikki P et al.: No evidence for measles, mumps, and rubella vaccine-associated inflammatory bowel disease or autism in a 14-year prospective study [letter]. Lancet 1998; 351 (9112): 1327-1328.
52. Fombonne E, Zakarian R, Bennett A et al.: Pervasive developmental disorders in Montreal, Quebec, Canada: Prevalence and links with immunizations. Pediatrics 2006; 118: 139-150.
53. Honda H, Shimizu Y, Rutter M: No effect of MMR withdrawal on the incidence of autism: a total population study. Journal of Child Psychology and Psychiatry 2005; 46: 572-579.
54. Richler J, Luyster R, Risi S et al.: Is there a 'regressive phenotype' of autistic spectrum disorder associated with the measles-mumps-rubella vaccine? A CPEA study. Autism Dev Dis 2006; 36: 299-316.
55. Smeeth L, Hall AJ, Fombonne E et al.: 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.
56. Uchiyama T, Kurosawa M, Inaba Y: MMR-Vaccine and Regression in Autism Spectrum Disorders: Negative Results Presented from Japan. J Autism Dev Disord 2007; 37 (2): 210-217.
57. Russell B: The Basic Writings of Bertrand Russell. New York, Routledge 2009.