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News › MMR and the incidence of autism recorded by GP's: a time trend analysis
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Autism Statistics: MMR and the incidence of autism recorded by GP's: a time trend analysis
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Posted by Sylvia on Monday, November 17, 2003 (10:38:31)
(British Medical Journals) Paper by James A Kaye, epidemiologist, Maria del Mar Melero-Montes, epidemiologist, Hershel Jick, associate professor of medicine.
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 5 year old boys; coverage (prevalence) of MMR vaccination in the same birth cohorts.
Results: The incidence of newly diagnosed autism increased sevenfold, 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 4 to 14) per 10 000 for boys born in 1988 to 29 (20 to 43) 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 among 2 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.
Introduction
The possibility that the mumps, measles, and rubella (MMR) vaccine may be causally related to the risk of autism is currently causing substantial concern. This proposition originated primarily from a publication by Wakefield et al in 1998 that described 12 case reports of children who were diagnosed with ileal-lymphoid-nodular hyperplasia followed by behaviour disorders that were clinically diagnosed as representing autism.1 In eight of 12 children the behaviour disorder was "linked" in time with MMR vaccination by the parents or the child's physician.
In June 1999 Taylor et al published in the Lancet the results of a study in which they identified children diagnosed as having autism in the North East Thames region for birth cohorts from 1979 to 1992.2 They reported that the incidence of autism started to increase in children born in the late 1980s and increased dramatically in those born from 1989 to 1992. They also provided estimates of the coverage (prevalence) of MMR vaccination from 1987 to 1995, which rose to over 90% by 1988-9.
They found no temporal association between MMR vaccination and the incidence of autism within one to two years of vaccination, and there was no "clustering" of cases in the two to four months after vaccination.
In a subsequent letter to the Lancet's editor Wakefield described the study by Taylor et al2 as containing a "fundamental flaw" and cited data from the United Kingdom (north west London) and the United States (California) based on the time trend of autism occurrence by birth cohort in relation to the introduction of the MMR vaccine.3 In both areas a dramatic increase in the incidence of autism was reported in temporal association with the rapid introduction of the vaccine.
We used the UK general practice research database (GPRD) to evaluate further the temporal relation of MMR vaccine and the incidence of autism.
Click here to read the full report
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Posted by Sylvia on Monday, November 17, 2003 (10:38:31) (19937 reads)
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