What was the impact of the alleged vaccine-autism connection?

What the public didn't know in 1998 was that the now-retracted study, which involved just 12 children, would turn out to have some serious flaws—and even to contain apparently falsified data. The 12 years between its publication and its retraction, however, left a lot of time for the unfounded and never-confirmed vaccine-autism link to take hold in the minds of worried parents—and thus for vaccination rates to suffer.

In 1997, the year before the paper was published, measles vaccination rates in the United Kingdom were over 91%. They started to fall in 1998 and in 2003-2004 reached a nadir of just 80%, although rates were even lower than that in specific areas. Only in recent years have MMR vaccination rates started climbing again in the U.K., reaching about 90% in 2013.

As a result of a paper published in 1998, MMR vaccination rates dropped Europe. The dotted line indicates the year in which Wakefield and colleagues published a paper alleging a connection between the MMR vaccine and autism. © Tangled Bank Studios; data from the National Health Service of the United Kingdom

The vaccine-autism question: A timeline

Here are some highlights along the scientific journey the vaccine-autism hypothesis made from its 1998 publication in The Lancet to today. The American Academy of Pediatrics has compiled an expanded list of relevant studies.

1998-The Lancet publishes a paper by Wakefield et al. titled "Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children." A press conference and interview in which Wakefield says it is his "feeling that the…risk of this particular syndrome developing is related to the combined vaccine, the MMR, rather than the single vaccines" set off a media storm.

1999—A U.S. Food and Drug Administration review of the vaccine preservative thimerosal, which contains mercury, finds no evidence of its causing neurological harm, but the agency recommends the precautionary removal of the agent from vaccines administered to infants.

2001—Thimerosal is removed from childhood vaccines on the U.S. market.

—The Journal of the American Medical Association publishes "Time trends in autism and in MMR immunization coverage in California" by Dales et al. These authors looked for and found no association between MMR vaccination rates in young children and increased autism occurrence.

—Pediatrics publishes "No evidence for a new variant of measles-mumps-rubella-induced autism." by Fombonne et al. In this study of 96 children with pervasive developmental disorders, the authors found no evidence of a specific syndrome being related to whether or not they had received the MMR vaccine.

2002—The British Medical Journal publishes "Measles, mumps, and rubella vaccination and bowel problems or developmental regression in children with autism: population study" by Taylor et al. This study of 473 children with autism who were born between 1979 and 1998 offered "further evidence against a link between MMR and autism." The authors found no differences in regression or bowel symptoms in those born before and after the introduction of the MMR vaccine.

—Pediatrics publishes "Neurologic disorders after measles-mumps-rubella vaccination" by Makela et al. This study of 535,544 children in Finland found no link between MMR vaccination and autism.

—The New England Journal of Medicine publishes "A population-based study of measles, mumps, and rubella vaccination and autism" by Madsen et al. These authors describe "strong arguments" against the hypothesis that the MMR vaccine causes autism, based on an analysis of data from 537,303 children in Denmark, 82% of whom had received the MMR vaccine.

2003—The Journal of the American Medical Association publishes "Association between thimerosal-containing vaccine and autism" by Hviid et al. These authors, using data from 467,450 children born in Denmark, found no link between autism risk and vaccines containing thimerosal.

2004—Of the 13 authors on the 1998 Wakefield paper, ten formally retract its interpretation, stating a wish to make clear that the paper established "no causal link" between the MMR vaccine and autism.

—The Institute of Medicine of the United States' National Academies issues a report from its Immunization Safety Review Committee, which concludes that vaccines don't cause autism.

2007—The New England Journal of Medicine publishes "Early thimerosal exposure and neuropsychological outcomes at 7 to 10 years" by Thompson et al. These authors looked for links between early thimerosal exposure and neuropsychological outcomes in a group of 1,047 children aged seven to ten years and found no association.

2010—The Lancet, after an extensive investigation, including investigative work by journalist Brian Deer, issues a formal retraction of the 1998 Wakefield paper.

—The U.K,'s General Medical Council strikes Andrew Wakefield from the medical register (the U.K. equivalent of stripping a medical license), concluding, according to reports, that he had been "dishonest, irresponsible, and showed callous disregard for the distress and pain of children" in conducting the MMR-autism study.

—Pediatrics publishes "On-time vaccine receipt in the first year does not adversely affect neuropsychological outcomes" by Smith et al. This study of more than 1,000 children born between 1993 and 1997 found that on-time vaccination was associated with better performance on a number of neuropsychological tests.

—Pediatrics publishes "Prenatal and infant exposure to thimerosal from vaccines and immunoglobulins and risk of autism" by Price et al. This study of over 1,000 children found no increase in autism outcomes among children who had received thimerosal-containing vaccines, compared to those who had not.

2013—A major measles outbreak in Wales is linked to regional response to the 1998 Wakefield paper, which led to reduced measles vaccination rates in the region affected by the outbreak.

—The Journal of Pediatrics publishes "Increasing exposure to antibody-stimulating proteins and polysaccharides in vaccines is not associated with risk of autism" by DiStefano et al. This study of more than 1,000 children found no link between the number of antigens in vaccines and autism, and thus no support for the "too many, too soon" school of thought.

2014—Vaccine publishes "Vaccines are not associated with autism: An evidence-based meta-analysis of case-control and cohort studies" by Taylor et al. This meta-analysis of ten studies covering more than 1.2 million children finds no links between autism and MMR vaccination, mercury, thimerosal, or vaccination generally.