There has never been a safer time to be born in Ireland and as a Paediatrician the changes that have occurred in a generation are both remarkable and reassuring. Polio, diphtheria and infant deaths from pneumonia or tuberculosis are almost historical curiosities for today's informed, internet friendly, parents of 2.2 children. Ireland has one of the lowest infant mortality rates in the world despite the occurrence of major social changes, with persisting significant levels of deprivation, the demise of both religion and the extended family, an increase in single parent families and the explosion in drug use with its attendant baggage of social chaos, crime, HIV and Hepatitis C infection. This improvement in infant mortality rates is not just a stroke of good fortune but has resulted from a combination of improved living standards (for the majority), education, nutrition and the health care services which have seen a fall in both neonatal and post neonatal (SIDS and infectious) deaths. It is remarkable that against this background there continues to be a debate about the possible link between immunization, specifically the 3:1 vaccine and SIDS. That this could occur, despite the overwhelming evidence to the contrary, is an indictment of the medical profession's poor communications/presentational skills. 

Worldwide evidence discounts vaccine as risk factor

Obviously the peak age of occurrence of SIDS (2-4 months) coincides with immunisation so inevitably some infants will die from SIDS within days of receiving, usually, the 3:1 vaccine. However, if immunisation does increase the risk of SIDS then the number of SIDS occurring in a vaccinated population will be higher than in a comparable unvaccinated population. There are many large epidemiologic databases which not only do not support the suggestion that immunisation increases the risk of SIDS but often show less SIDS in immunised populations compared to unimmunised populations. An Australian study found the majority of SIDS deaths occurring in unimmunised infants.¹ A large North American study, of 800 SIDS cases and matched controls, found less SIDS cases occurred in immunised infants.² A New Zealand study, of 485 SIDS and 1800 control infants, found immunisation to significantly reduce the risk of SIDS.³ Large, SIDS related, epidemiological databases have also been established in Germany, France, Scotland, England, Norway and Sweden, and in none has immunisation emerged as a risk factor for SIDS with the majority finding less SIDS among immunised infants. In 1992 Ireland established a National Register of all Infant Deaths which also shows no association between immunisation and SIDS but rather a clear link between socioeconomic deprivation, and the associated low immunisation rates, and SlDS.⁴ The Irish National SIDS Register has been conducting a prospective case/control study which shows a highly significant association between lack of vaccination and SIDS. In 1994/95 44% of Irish SIDS infants received no vaccinations compared to 10% of the control group(p<0.002) with this sort of difference persisting for the number of vaccinations received. A single study, comparing 118 SIDS to 332 controls, found a very slight, non-significant, increase in the number of SIDS cases in immunised infants.⁵ However, the control group in this study were not well matched to the SIDS group invalidating this study. A review of the relevant literature, in the American Journal of Epidemiology in 1992, concluded that most published studies have reported a deficit of SIDS among vaccinees.⁶ Finally over the past 5 years the SIDS rate in England and Wales has fallen to an all time low of 0.7/1000 live births at a time when vaccination rates of >90% are the norm. So we can unambiguously state that immunizations are not associated with an increased ask of SIDS. 

Poor communication

The message, for me, is that while we may think that we are good communicators the fact that this controversy is still rattling around means that we are not. We need to become more proactive in getting clear and unambiguous health advice into the public domain and accept that the days of unquestioning acceptance of statements from "experts" is gone. Where there is solid data supporting our statements this should be clearly presented and debated if needed. Finally anybody, from a professor of paediatrics to a doctor of animal psychopathology, making a statement on a matter of public health should be asked to detail the data on which the statement is based including the methodology of any studies being presented. 
Tom Matthews,
Professor of Paediatrics,
Rotunda Hospital,
Dublin 1.

References

1. Byard RW, et al. Vaccination and SIDS: information from the South Australian SIDS database. Med J Aus 1995;163:443-4. 
2. Hoffmann HJ, et al. Diphtheria-tetanus-pertussis immunisation and sudden infant death: results of the National Institute of Child Health and Human Development Co-operative Epidemiological Study of Sudden Infant Death Syndrome risk factors. Pediatrics 1987;79:598-611. 
3. Mitchell EA, et al. Immunisation and the sudden infant death syndrome. Arch Dis Child 1995;73:498-501. 
4. Annual Reports of The National SIDS Register. St. Georges Hall, The Children's Hospital, Temple St, Dublin 1:1992-95. 
5. Jonville-Bera AP, et al, Sudden Infant Death Syndrome and Diphtheria tetanus-pertussis-poliomyelitis vaccination status. Fundam Clin Pharmacol 1995;9:263-270. 
6. Fine PEM, Chen RT. Confounding in studies of adverse reactions to vaccines. Am J Epidem 1992;136:121-35.