美国儿童疫苗第一章 疫苗和自闭症

前面说到疫苗安全性的问题，不得不谈谈疫苗跟自闭症的关系。虽然其实是没关系，但是这话没法说成“谈谈疫苗跟自闭症的没关系”不是？
这个话题由于比较热门，关心的人比较多，涉及比较多的疫苗，所以单独讨论。
首先先了解一下自闭症（autism）。由于我不是这方面的专家，也是查文献，放狗搜的结果，难免有不当之处。知道版上有这方面的专家，如果我说的有错误，误导之处，请大家指出，我来改正。
自闭症，英文叫做autism spectrum disorders（ASDs）实际上包括autistic disorder（AD），asperger syndrome（AS）和Pervasive Developmental Disorder-Not Otherwise Specified（PDD-NOS）。1943年Johns Hopkins University的一个医生第一次描述了这个病的症状（Kanner L. Autistic disturbances of affective contact. Nerv Child. 1943;2: 217–250）。1944年，奥地利的另外一个儿科医生也独立发现了这个病（Asperger H. Die “autistischen psychopathen” im kindesalter. Arch Psychiatr Nervenkr. 1944;117:76–136）。三十多年后，到1980年，infantile autism这个词才第一次正式进入精神疾病的诊断标准（American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, 3rd Edition (DSM-III). Washington,
DC: American Psychiatric Association; 1980）。ASDs的诊断在之后的30年中发生了几次大的变化。The Diagnostics and Statistics Manual of Mental Disorders (DSM) 是美国精神病协会发表的精神疾病的诊断标准手册（http://en.wikipedia.org/wiki/Diagnostic_and_Statistical_Manual_of_Mental_Disorders）。自闭症就是在这个手册提供的标准下来诊断的。DSM共发布了以下6个版本：
1. 1952年的DSM-I ：虽然ASD被认为是一种疾病，但是没有作为单独的疾病来诊断。有自闭症症状的孩子可能被诊断为schizophrenic, childhood type。
2. 1968年的DSM-II ：同上。
3. 1980年的DSM-III ：ASD终于成为单独诊断的疾病。但是只有6条诊断标准。必须全部符合，才能诊断自闭症。
4. 1987年的DSM-III-R ：增加了儿童的ASD。
5. 1994年的DSM-IV ：ASDs新的诊断标准增加了Asperger’s Disorder, Rett’s Disorder, Childhood Disintegrative Disorder, and Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS) 这4个新的种类。
6. 2000年的DSM-IV-TR （这个是现在2010年使用的版本）：形成ASDs现在的诊断标准。
具体的诊断标准如果有空，我会在单开帖子说明。以上的内容参考了以下这些网站的内容：
（http://autismaspergerssyndrome.suite101.com/article.cfm/history_of_autism_in_the_dsm）
（http://www.brighthub.com/mental-health/autism-pdd/articles/62832.aspx）
（http://www.theautismeducationsite.com/2010/06/11/history-of-autism-in-the-dsm-dsm-i-to-dsm-iv/）
从这里大家可以看到，自闭症的诊断在过去的几十年里从无到有，从少到多，范围被不断扩大，囊括越来越多的subtypes。同时由于公众，医务工作者，政府，学校，媒体对这个的关心越来越多，也有更多的比较轻微的病人被诊断出来，有机会得到治疗。这个变化，至少是部分导致了自闭症患者的大量增加。这里有篇文章专门讨论这个问题：http://www.wellsphere.com/autism-autism-spectrum-article/diagnostic-change-and-the-increased-prevalence-of-autism/798393
其结论是：“It does demonstrate that factors like diagnostic change and accretion are real and significant… Just because the number of people identified with autism went up doesn’t mean that all of that number is due to a real increase in the number of people who are autistic.”就是说，诊断标准的改变确实明显影响自闭症患者的诊断数量。当然不能排除自闭症的真实数量确实在增加，但是到底增加多少还难以确定。

现在来看看自闭症和疫苗的关系。我分别列出支持和反驳的证据。但是首先要说明的是，仅仅时间上的巧合，是不足以构成因果关系的。就是说，时间的先后次序是因果关系的“必要非充分条件”。我会focus on已经publish的研究成果。但是由于这个问题非常热门，所以研究非常多，我不可能列出全部的证据，只能尽我所能地列出一些比较有说服力的成果。

首先是支持疫苗（主要是MMR）导致或者有可能导致自闭症的证据：

1. Andrew Wakefield发表在1998年2月28日的柳叶刀杂志上的文章：http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2897%2911096-0/fulltext
应该算这个问题的开山之作。他在这篇文章中报道了12个儿童的研究结果，认为MMR可能引起消化道炎症反应，而这些消化道症状有可能引起自闭症。但是之后2004年Sunday Time揭露他在发布这个研究报告前收受反疫苗律师贿赂，所以于2010年1月28日“the British General Medical Council (GMC) … ruled that Wakefield had "failed in his duties as a responsible consultant", acted against the interests of his patients, and acted "dishonestly and irresponsibly" in his controversial research.”之后2010年2月2号，柳叶刀杂志收回了他的那篇论文。5月被英国剥夺医生执照。这个案子的详细经过请见wikipedia（http://en.wikipedia.org/wiki/Andrew_Wakefield）。
2. 在这篇文章发表之后，无数的研究者进行了大规模的临床和实验室研究，但是没有一个能够重复Andrew Wakefield的结果。而任何试图证明二者联系的研究也都是否定性结论。
3. 网上的accusation全部based on患者个人的testament，“专家”意见，却无法从研究中得到证实。比如：
http://www.dailymail.co.uk/health/article-376203/Former-science-chief-MMR-fears-coming-true.html
http://www.drbriffa.com/2008/05/30/why-the-mmr-autism-war-is-not-over
对了，还可以参见白云同学发布的youtube录像，lol

现在看看否定疫苗和自闭症关系的证据。跟大多数反疫苗人士的claim相反，这个问题在Wakefield的paper出来之后立刻引起学界的重视。为此不同国家、不同机构、不同研究者做了大量的临床和实验室研究。这些研究主要为了解决两个问题，第一是建立疫苗或者含汞疫苗的安全性问题。开始主要是为了研究MMR和自闭症的问题，但是所有研究都否定了这一结论，所以研究被扩展到疫苗和任何神经系统损害的关系问题。事实上，结果仍然是否定的。第二为了解决疫苗引起自闭症的生物学解释问题。由于研究发现疫苗根本不导致神经系统损害，所以这个问题根本无从谈起。相关研究数不胜数，偶只能按照时间顺序择要列举。并且，由于篇幅所限，不对每篇文章做详细讨论，只列举主要结论：
1. Immunization Safety Review: Vaccines and Autism. Institute of Medicine (US) Immunization Safety Review Committee. Washington (DC): National Academies Press (US); 2004.
主要结论：“The committee concludes that the body of epidemiological evidence favors rejection of a causal relationship between the MMR vaccine and autism. The committee also concludes that the body of epidemiological evidence favors rejection of a causal relationship between thimerosal-containing vaccines and autism.”
美国NIH下属的国家医学院IOM组织了一个专门的研究委员会，来研究疫苗的安全性问题，主页在这里：http://www.iom.edu/Activities/PublicHealth/ImmunizationSafety.aspx。这个委员会并非专门为疫苗和自闭症建立，而是为了为了独立研究更广泛的疫苗副作用和安全问题而建立的。但是由于公众对自闭症的担忧，这个委员会于2001年和2004年两次发表对于这个问题的研究报告。得出以上结论。这个结论是目前关于这个问题最常被引用，也是最权威的结论。这个报告的详细内容请见：
2001年报告：http://www.nap.edu/catalog.php?record_id=10101
2004年报告：http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=nap10997&part=a2000af8fddd00024#a2000af8fddd00036。
2. Ned Tijdschr Geneeskd. 2004 Feb 21;148(8):364-71. [Childhood vaccinations anno 2004. II. The real and presumed side effects of vaccination] [Article in Dutch] Rümke HC, Visser HK. Vaxinostics BV, Rotterdam, p/a Erasmus Medisch Centrum, locatie Sophia, Postbus 2060, 3000 CB Rotterdam. h.rumke@erasmusmc.nl
荷兰是个非常严谨的国家。从1962年开始，全国每个孩子所有的疫苗反应都被记录下来，保存到一个中央数据库，由the National Institute of Health and Environment (RIVM)来保存和分析。1983年，荷兰又建立了一个专门的委员会来研究疫苗安全问题。由于有这个完整的数据系统，荷兰可以很容易地分析疫苗引起的各种可能的副作用。2004年荷兰的研究证明疫苗和包括自闭症在内的一系列可能副作用无关：“Careful and extensive investigations have shown that such hypotheses could not be supported. Examples are allergic diseases as asthma, diabetes mellitus, multiple sclerosis (after hepatitis B vaccination), autism and inflammatory bowel disease (after MMR vaccination) and sudden infant death syndrome.”。
可惜的是，这个报告是用荷兰语写的，偶一个字都不认识。只能从翻译成英文的文章摘要中得到结论。
3. J Child Psychol Psychiatry. 2005 Jun;46(6):572-9. No effect of MMR withdrawal on the incidence of autism: a total population study. Honda H, Shimizu Y, Rutter M. Yokohama Rehabilitation Center, Yokohama, Japan.
报告全文：http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7610.2005.01425.x/full。
这是2005年日本的的一个研究报告。日本从1993年开始由于其他原因不使用MMR疫苗，而把三个疫苗分开打。所以在2005年可以回顾性调查当年打了MMR和没打MMR的人群中的自闭症发病率有没有差别。事实比较出人意料，“The MMR vaccination rate in the city of Yokohama declined significantly in the birth cohorts of years 1988 through 1992, and not a single vaccination was administered in 1993 or thereafter. In contrast, cumulative incidence of ASD up to age seven increased significantly in the birth cohorts of years 1988 through 1996 and most notably rose dramatically beginning with the birth cohort of 1993.”这个的意思是1988年到1992年打了MMR的人群大大下降了1993年之后再也没有一个人打过MMR，而1993年禁止使用MMR之后发病率反而升高了，特别是1993年之后出生的这些孩子。这个报告发现的现象跟前面日本的另外一篇报告结果相近：“These results suggest a decreased risk of developing ASD with MMR compared to monovalent antigens.”（Jpn J Infect Dis. 2003 Jun;56(3):114-7. An epidemiological study on Japanese autism concerning routine childhood immunization history. Takahashi H, Suzumura S, Shirakizawa F, Wada N, Tanaka-Taya K, Arai S, Okabe N, Ichikawa H, Sato T. Institute for International Cooperation, Japan International Cooperation Agency, Tokyo 162-8433, Japan. 全文的link在：http://www.nih.go.jp/JJID/56/114.pdf）
当然作为科学报告，作者不会建议大家打疫苗预防自闭症，但是其结论是相似的：“The significance of this finding is that MMR vaccination is most unlikely to be a main cause of ASD, that it cannot explain the rise over time in the incidence of ASD, and that withdrawal of MMR in countries where it is still being used cannot be expected to lead to a reduction in the incidence of ASD.”
4. N Engl J Med. 2002 Nov 7;347(19):1477-82. A population-based study of measles, mumps, and rubella vaccination and autism. Madsen KM, Hviid A, Vestergaard M, Schendel D, Wohlfahrt J, Thorsen P, Olsen J, Melbye M. Danish Epidemiology Science Center, Department of Epidemiology and Social Medicine, Arhus, Denmark.
原文在此：http://www.nejm.org/doi/pdf/10.1056/NEJMoa021134。
这个是丹麦的一个研究。北欧好像都有比较完整的国家医疗记录，做这种流行病学研究非常方便，呵呵。由于丹麦所有孩子的医疗都必须报告存入这个Danish National Board of Health，而且所有孩子的精神疾病诊断都存入Danish Psychiatric Central Register, 所以每个孩子的疫苗和精神疾病都有记录可查。这个研究是对照了1991年到1998年间出生的孩子中打了MMR疫苗和没打MMR疫苗的孩子的自闭症发病率。结果是：“the relative risk of autistic disorder in the group of vaccinated children, as compared with the unvaccinated group, was 0.92.”就是说比较而言，如果没打MMR发生自闭症的危险性是1的话，打了MMR发生自闭症的危险性是0.92 （0.68-1.24）。这里面如果大于1那么危险性越大，越小危险性也越小。这个。。。竟然跟日本人的结果相似，打疫苗竟然得自闭症的好像危险性还小点儿。当然从统计上说，没有显著差异，所以不能用打疫苗预防自闭症。文章的结论是：“This study provides strong evidence against the hypothesis that MMR vaccination causes autism.”证据不支持MMR疫苗引起自闭症。
5. Pediatrics. 2004 Feb;113(2):259-66. Age at first measles-mumps-rubella vaccination in children with autism and school-matched control subjects: a population-based study in metropolitan atlanta. DeStefano F, Bhasin TK, Thompson WW, Yeargin-Allsopp M, Boyle C. National Immunization Program, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA.
原文在此：http://pediatrics.aappublications.org/cgi/content/full/113/2/259。
在IOM的2001年关于疫苗和自闭症的第一份报告（Stratton K, Gable A, McCormick M, eds. Immunization Safety Review: Measles-Mumps-Rubella Vaccine and Autism. Washington, DC: National Academy Press; 2001）（我前面提到的是IOM发表的关于这个问题的第二份专题报告）发布后CDC也进行了大规模的临床调查（当然，阴谋论者不相信美国政府机构的调查，不信的请无视这条证据）。这个调查的目的是分析除了全部儿童之外，是否不同注射年龄会有影响。结论是：“…overall, the age at time of first MMR administration was similar among case and control children.”

这样的研究太多了，下面我只列出结论和报告的名称，不再讨论。
6. DeWilde S, Carey IM, Richards N, Hilton SR, Cook DG. Do children who become autistic consult more often after MMR vaccination? British J Gen Pract. 2001; 51(464): 226–7.
7. Pediatrics. 2002 Nov;110(5):957-63. Neurologic disorders after measles-mumps-rubella vaccination. Mäkelä A, Nuorti JP, Peltola H. Hospital for Children and Adolescents, Helsinki University Central Hospital, Helsinki, Finland.
芬兰的一个研究。主要结论是：“We did not identify any association between MMR vaccination and encephalitis, aseptic meningitis, or autism.”
8. Jpn J Infect Dis. 2003 Jun;56(3):114-7. An epidemiological study on Japanese autism concerning routine childhood immunization history. Takahashi H, Suzumura S, Shirakizawa F, Wada N, Tanaka-Taya K, Arai S, Okabe N, Ichikawa H, Sato T. Institute for International Cooperation, Japan International Cooperation Agency, Tokyo 162-8433, Japan.
日本的一个研究。我前面在3中提到这个研究。
9. BMJ. 2002 Feb 16; 324(7334):393-6. Measles, mumps, and rubella vaccination and bowel problems or developmental regression in children with autism: population study. Taylor B, Miller E, Lingam R, Andrews N, Simmons A, Stowe J. Centre for Community Child Health, Royal Free and University College Medical School, University College London Royal Free Campus, London.
英国的一个研究。结论是：“These findings provide no support for an MMR associated "new variant" form of autism with developmental regression and bowel problems, and further evidence against involvement of MMR vaccine in the initiation of autism.”
10. Pediatr Infect Dis J. 2010 May; 29(5):397-400. Lack of association between measles-mumps-rubella vaccination and autism in children: a case-control study. Mrozek-Budzyn D, Kiełtyka A, Majewska R. Department of Epidemiology and Preventive Medicine, Jagiellonian University, Collegium Medicum, Krakow, Poland.
波兰的一个研究。结论是：“The study provides evidence against the association of autism with either MMR or a single measles vaccine.”
11. PLoS One. 2008 Sep 4; 3(9):e3140. Lack of association between measles virus vaccine and autism with enteropathy: a case-control study. Hornig M, Briese T, Buie T, Bauman ML, Lauwers G, Siemetzki U, Hummel K, Rota PA, Bellini WJ, O'Leary JJ, Sheils O, Alden E, Pickering L, Lipkin WI. Center for Infection and Immunity, Mailman School of Public Health, Columbia University, New York, New York, United States of America.
美国的一个研究。结论是：“This study provides strong evidence against association of autism with persistent MV RNA in the GI tract or MMR exposure.”
这样的研究数不胜数，我就不一一列举了。有兴趣的同学可以自己搜索pubmed（http://www.ncbi.nlm.nih.gov/pubmed）。到今天为止，搜索“MMR autism”有超过200篇文章；搜索“vaccine autism”有超过500篇文章。这些报告来自世界各地，不仅仅是美国。从目前的证据来看，反对疫苗和自闭症关系的证据具有压倒性优势，结论是清楚的。在目前看来，打疫苗包括MMR跟发生自闭症没有因果关系。这个结论已经是学界共识。目前看来没有新的证据出现之前已经不值得再为这个问题做进一步研究。但是这个话题的兴起在反疫苗运动的推波助澜下，对公共健康已经造成了不可逆转的损失。部分地区，包括英国，日本，美国等由于MMR的注射率下降，开始出现measles的局部爆发，有孩子也因感染死亡：
http://www.timesonline.co.uk/tol/news/uk/health/article701459.ece
http://news.bbc.co.uk/2/hi/health/7753210.stm

这个问题就说到这里。总结一句，根据现在的自闭症诊断标准，MMR和自闭症无关，疫苗和自闭症无关，这个是大量数据支持的定论。对的，我没有笔误，是“定论”！建议反疫苗的同学换个新话题吧。
现在学界研究的一个重要题目事实上是为什么会有人反疫苗？对公共健康造成了什么样的损失？如何有效地说服家长给孩子按计划打疫苗？
关于MMR的其他副作用和相关疾病的情况，我在MMR一章中再详细介绍。

第二个问题是汞和自闭症的关系。汞是已知的具有神经毒性的重金属。汞的急性中毒会引起神经毒性，肾毒性和肺损害等症状：
http://emedicine.medscape.com/article/819872-overview
http://en.wikipedia.org/wiki/Mercury_poisoning
http://www.medicinenet.com/mercury_poisoning/article.htm
http://www.epa.gov/mercury/effects.htm
这些网站都有比较详细的症状描述，限于篇幅，偶就不一一转抄了。但是，在美国大家接触汞的主要来源包括：海产品，牙科补牙，宗教活动（嘻嘻，EPA说的，不知道包括不包括炼丹术？）http://www.epa.gov/mercury/exposure.htm。
由于汞在急慢性中毒是确实有中枢神经系统毒性，很多人因此也怀疑疫苗中的汞是否会引起自闭症。疫苗中的汞过去是作为preservative来用的。就是说是防腐剂。原因是在疫苗发展的早期，曾经有过疫苗因为细菌污染而导致的死亡的记录。因此之后所有的疫苗都被要求加入防腐剂。
在美国等发达国家除了流感疫苗已经没有含汞疫苗。但是在发展中国家，由于技术和经费原因仍然要依赖含汞疫苗。
因此有研究认为虽然疫苗中汞的神经毒性不清楚，但是应该慎重起见，尽量帮助发展中国家过渡到无汞疫苗。作为发达国家也值得为此进一步研究。参见以下研究：
• Clin Chim Acta. 2010 Jul 16. Making sense of epidemiological studies of young children exposed to thimerosal in vaccines. Dórea JG.
• Acta Neurobiol Exp (Wars). 2010;70(2):187-95. Does thimerosal or other mercury exposure increase the risk for autism? A review of current literature. Schultz ST. University of Texas, Health Science School, San Antonio, TX, USA.
• Neurotox Res. 2010 Jul;18(1):59-68. Epub 2009 Sep 16. Are neuropathological conditions relevant to ethylmercury exposure? Aschner M, Ceccatelli S. Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
• J Toxicol Environ Health A. 2007 May 15;70(10):837-51. A case series of children with apparent mercury toxic encephalopathies manifesting with clinical symptoms of regressive autistic disorders. Geier DA, Geier MR. Institute of Chronic Illnesses, Inc., Silver Spring, Maryland, USA.

另外一些研究直接否认二者的关系：
• Clin Infect Dis. 2009 Feb 15;48(4):456-61. Vaccines and autism: a tale of shifting hypotheses. Gerber JS, Offit PA. Division of Infectious Diseases, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104-4399, USA.
• J Intellect Disabil Res. 2009 Feb;53(2):115-24. Epub 2008 Nov 27. Regression of language and non-language skills in pervasive developmental disorders. Meilleur AA, Fombonne E. Université de Montréal, Rivière-des-Prairies Hospital, Montreal, QC, Canada.
• Arch Gen Psychiatry. 2008 Jan;65(1):15-6. Thimerosal disappears but autism remains. Fombonne E. Department of Psychiatry, Montreal Children's Hospital, 4018 Ste Catherine W, Montreal, QC H3Z 1P2, Canada.
• N Engl J Med. 2007 Sep 27;357(13):1281-92. Early thimerosal exposure and neuropsychological outcomes at 7 to 10 years. Thompson WW, Price C, Goodson B, Shay DK, Benson P, Hinrichsen VL, Lewis E, Eriksen E, Ray P, Marcy SM, Dunn J, Jackson LA, Lieu TA, Black S, Stewart G, Weintraub ES, Davis RL, DeStefano F; Vaccine Safety Datalink Team. National Center for Immunizations and Respiratory Diseases, Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.

相关的研究非常多，我就不一一列举了。这个问题在业界还有争议。仍在继续研究。
好在美国的儿童疫苗，已经不含汞了。只有部分成人疫苗，包括流感疫苗，破伤风，DTwP（不是孩子们用的DTaP）含有thimerosal。http://www.vaccinesafety.edu/thi-table-10-0223.pdf。

历史也是一件有意思的事情。比如这篇文章：
http://ajph.aphapublications.org/cgi/content/full/98/2/244?ijkey=2862beee4372b08b70447f72206c6e3caef86e35
Am J Public Health. 2008 Feb;98(2):244-53. Epub 2008 Jan 2. Mercury, vaccines, and autism: one controversy, three histories. Baker JP. Trent Center for Bioethics, Humanities, and History of Medicine, Duke University School of Medicine, Box 3040, Duke University Medical Center, Durham, NC 27710, USA.
介绍了汞作为疫苗防腐剂的发展历史，汞安全性研究的历史，和汞与自闭症关系的发展史（Why was the mercury-containing preservative thimerosal introduced in infant vaccines in the first place? Why was its use not questioned until the late 1990s, long after the toxic effects of mercury had been recognized? Why was autism perceived to be "epidemic" in the 1990s, and how did it become linked to vaccines in the public’s mind?）
这三个问题都非常有趣，能够帮助我们理解汞的安全性问题的由来。如果大家有空的时候能够读一下，肯定受益匪浅。
俺就偷懒了，结论照抄，作为这一章的结束语：
At this point, it is fair to ask whether this narrative should more properly have focused on the story of the thimerosal controversy since 1999. Has not a new group of actors, including members of Congress, professional groups, antivaccine organizations, and personal injury lawyers, assumed central relevance since that time? Is it really that necessary to understand the long-term historical trends that converged just prior to the 1999 joint statement?
There are three answers, each corresponding to one of the historical streams already examined. The first is directed at the insinuation prevalent on the Internet that thimerosal was a dubious product smuggled into vaccines by avaricious drug companies bent on profits rather than the welfare of children. A more sober assessment would suggest that thimerosal was the result of ethical scientific and corporate research in the 1920s and 1930s, specifically to improve vaccine safety. Despite questions regarding its efficacy, it has performed well in practice and posed toxicity so low as to be considered negligible until recent years.
The second point concerns the history of mercury poisoning. Central to the public story of thimerosal has been a battle over the meaning of "mercury." Those in the scientific community take it as axiomatic that all forms of mercury are not created equal; in particular, there are good reasons to believe that the ethylmercury used in vaccines is very different from the methylmercury studied in environmental science. In public discourse, however, such distinctions are subsumed under a single entity, mercury, with a long and very public history. Perhaps unfairly, history has endowed mercury in all of its forms with a notoriety that is not easy to erase, as will quickly be discovered by any pediatrician trying to convince an anxious mother that a "trace" of mercury in a vaccine is safe. One cannot simply brush aside this perception in constructing policy.
Finally, however important personal injury lawyers, vaccine skeptics, and their allies in Congress may have been in shaping the thimerosal controversy since 1999, they did not create it. Parents within the "alternative" wing of the autism community were the primary agents in popularizing the concepts that autism had become epidemic and that vaccines were its cause. Jumping from the first to the second proposition may have been highly conjectural, but the question of whether the rise in autism is real or defined (or both) remains open to reasonable debate. There is genuine anger in the autism community that has fueled the polarization of the thimerosal debate, but this anger is best understood in terms of frustration with the medical and educational systems, not the cynical manipulation of lawyers.
Although historical understanding may not readily translate into policy guidelines, it is essential for those responsible for conducting and implementing such policy. A polarized debate both draws upon and contributes to polarized understandings of history. Participants within each of this story’s three streams judged the same data using different sets of assumptions, each shaped by history. Articulating and sharing these narratives represent a first step toward transcending the powerful boundaries shaping today’s vaccine controversies.