BMJ 2001; 322 doi: https://doi.org/10.1136/bmj.322.7284.460 (Published 24 February 2001) Cite this as: BMJ 2001;322:460
| A UK study compared MMR vaccination of children and rising prevalence of autism diagnoses in children. The study included 96 children with a pervasive developmental disorder born between 1992 and 1995 who received the MMR vaccine to those who did not receive the vaccine. No correlation was found between the prevalence of MMR vaccination and increase in risk of autism over time. |
Abstract
Objective
To estimate changes in the risk of autism and assess the relation of autism to the mumps,measles, and rubella (MMR) vaccine.
Design
Time trend analysis of data from the UK general practice research database (GPRD).
Setting
General practices in the United Kingdom.
Subjects
Children aged 12 years or younger diagnosed with autism 1988≠99, with further analysis of boys aged 2 to 5 years born 1988≠93.Main outcome measures Annual and age specific incidence for first recorded diagnoses of autism (that is, when the diagnosis of autism was first recorded) in the children aged 12 years or younger; annual, birth cohort specific risk of autism diagnosed in the 2 to 5year old boys; coverage (prevalence) of MMR vaccination in the same birth cohorts.
Results
The incidence of newly diagnosed autism increased seven fold, from 0.3 per 10 000 person years in 1988 to 2.1 per 10 000 person years in 1999. The peak incidence was among 3 and 4 year olds, and 83%(254/305) of cases were boys. In an annual birth cohort analysis of 114 boys born in 1988≠93, the risk of autism in 2 to 5 year old boys increased nearly fourfold over time, from 8 (95% confidence interval 4to 14) per 10 000 for boys born in 1988 to 29 (20 to43) per 10 000 for boys born in 1993. For the same annual birth cohorts the prevalence of MMR vaccination was over 95%.
Conclusions
Because the incidence of autism among2 to 5 year olds increased markedly among boys born in each year separately from 1988 to 1993 while MMR vaccine coverage was over 95% for successive annual birth cohorts, the data provide evidence that no correlation exists between the prevalence of MMR vaccination and the rapid increase in the risk of autism over time. The explanation for the marked increase in risk of the diagnosis of autism in the past decade remains uncertain.
Brian S. Hooker, Ph.D.
Study’s overview: This study was a time trend analysis, where researchers look to see if one variable increases or decreases in tandem with another factor over a period of time. The researchers looked at the rate of increase of autism diagnoses among children between 1988 and 1999, and then specifically boys born between 1988 and 1993 and the rate of MMR vaccine administration (uptake) during the same time periods. The authors claimed that there was no correlation despite a marked increase in autism incidence with time, because trends in MMR uptake remained unchanged.
Study’s flaws: Instead of defining autism incidence based on when the child was born, the study authors instead defined autism incidence based on diagnosis rate during diagnosis year with the denominator corrected for age of diagnosis. This method gives a bias towards autism diagnosed at younger ages and is not a true measure of autism incidence. Therefore, this section on the analysis is essentially meaningless in determining true autism incidence versus MMR uptake. The rate of MMR uptake remained steady at over 95% throughout the birth cohorts while the autism incidence (as measured by the researchers) increased sevenfold. MMR uptake could not possible proportionally increase as it was already a high 95%, so this type of temporal study sheds no light – it was de facto “proof” by design.
Conflicts of interest: The authors of this paper were residents at the Boston Collaborative Drug Surveillance Program, at Boston University School of Medicine. This program is supported in part by grants from AstraZeneca, Berlex Laboratories, Boehringer Ingelheim Pharmaceuticals, Boots Healthcare International, Bristol-Myers Squibb Pharmaceutical Research Institute, GlaxoWellcome, Hoffmann-La Roche, Janssen Pharmaceutica Products, R W Johnson Pharmaceutical Research Institute; McNeil Consumer Products, and Novartis Farmaceutica. Funding for their residency program is directly tied to those profiting from the vaccine companies their claims protect.