http://bmj.com/cgi/content/full/323/7305/163?view=full&pmid=11463692

Argument is too simplistic

EDITOR---Kaye et al analysed time trends in measles, mumps, and rubella (MMR) vaccine and the incidence of autism.1 Because the increase of autism is gradual whereas the prevalence of immunisation is constant, they argue that there is no evidence of an association. This argument, however, rests on the assumption that the rate of diagnosis rate each year after the onset of clinical symptoms is constant with respect to birth cohort and that a mild case has a constant chance of being diagnosed.

Altmann points out that 40% of cases have diagnosis delayed up to three years.2 Could increasing awareness of paediatricians and general clinicians of autism during this period account for the gradual increase? When the first unexpected extra cases were found in 1991-2, could that not have increased vigilance? As evidence, we point to the median age at diagnosis as reported by the authors. Except for 1993, there seems to be a trend towards earlier diagnosis. We exclude 1998-9 because the cohort then changed substantially, with several practices no longer providing information. Could Kaye et al show a test of trend from 1988 to 1997 to see whether there was a systematic decrease in age at diagnosis? Is it also possible to investigate the notion that average severity of cases was dropping over this time period?

Finally, was there a trend towards earlier vaccination, as can be seen in data from California?3 For example, did the percentage of vaccinations at less than 10 months increase over time?

We submit that the argument given by Kaye et al is too simplistic to reassure us that there is no link between MMR and autism. The current arguments in favour of the link, however, remain unconvincing. 4 5

Michael Edwardes, research fellow. 
Division of Clinical Epidemiology, Ross 4.06, Royal Victoria Hospital, 687 Pine Avenue West, Montreal, Province of Quebec, Canada H3A 1A1 michael.edwardes@clinepi.mcgill.ca

Marc Baltzan, consultant physician. 
Mount-Sinai Hospital, 5690 Cavendish, Cote-St-Luc, Montreal, Province of Quebec, Canada H4W 1S7

1.

Kaye JA, del Mar Melero-Montes M. Mumps, measles, and rubella vaccine and the incidence of autism recorded by general practitioners: a time trend analysis. BMJ 2001; 322: 460-463[Abstract/Full Text]. (24 February.)

2.

Altmann D. Autism and measles, mumps and rubella vaccine. Lancet 2000; 355: 409[Medline].

3.

Dales L, Hammer SJ, Smith NJ. Time trends in autism and in MMR immunization coverage in California. JAMA 2001; 285: 1183-1185[Medline].

4.

Wakefield AJ, Murch SH, Anthony A, Linell J, Casson DM, Malik M, et al. Ileal-lymphoid-nodular hyperplasia, non-specific colitis and pervasive developmental disorder in children. Lancet 1998; 351: 637-641[Medline].

5.

Wakefield AJ. MMR vaccination and autism. Lancet 1999; 354: 949-950[Medline].



ALL INFORMATION, DATA, AND MATERIAL CONTAINED, PRESENTED, OR PROVIDED HERE IS FOR GENERAL INFORMATION PURPOSES ONLY AND IS NOT TO BE CONSTRUED AS REFLECTING THE KNOWLEDGE OR OPINIONS OF THE PUBLISHER, AND IS NOT TO BE CONSTRUED OR INTENDED AS PROVIDING MEDICAL OR LEGAL ADVICE.  THE DECISION WHETHER OR NOT TO VACCINATE IS AN IMPORTANT AND COMPLEX ISSUE AND SHOULD BE MADE BY YOU, AND YOU ALONE, IN CONSULTATION WITH YOUR HEALTH CARE PROVIDER.