SIDS and the link with vaccination
To the Editor,
Fleming et al have used a case-control study method to investigate
the temporal association between infant vaccinations and SIDS.1 Promoters
of mass vaccination will use this study to support the notion that infant
vaccination may actually be a "protective" factor against SIDS.
It should be noted, however, that the "case-control study" is known
to be a relatively weak study method that can not be relied upon to either
prove or disprove an association between vaccination and SIDS. Firstly,
significant bias can result from the selection or elimination of cases or
controls. Secondly, it is difficult to measure risk for a particular
characteristic that is present in the majority of the population.2 An
example of this can be found in a case-control study from California
(USA), which found no association between babies sleeping prone and SIDS.3
And yet many other studies have found an significant association between
sleeping position and SIDS. It has been suggested that the reason why the
Californian study did not show an association was because at the time of
the study (pre 1992), the majority of babies in California (64%) were
sleeping prone.2 In the study by Fleming et al the vast majority of
babies over 3 months were vaccinated (93% of controls vs 79% of cases).1
Therefore since this study characteristic was present in the large
majority of the population, it may have had an effect on the final
results. So depending on the study methods used, it is possible for some
statistics to not present the true picture.
Another flaw with this study is that apart from infant sleeping
position, other important confounding factors were not accounted for.
Maternal smoking is strongly linked with SIDS but was not accounted for in
the final result.4 Breast-feeding is also considered to be a variable that
may reduce the risk of SIDS.5 Again, this factor was not considered. In a
family with a lower socioeconomic status, failure to vaccinate a child
would also be associated with an increased incidence of maternal smoking
and bottle-feeding. These important, yet unaccounted for, stress factors
may explain why an association between vaccines and SIDS was not found.
A case-control study of this nature does not prove or disprove that
vaccination is a cause of SIDS. But a large prospective cohort study,
taking into account other important variables, would provide us with much
firmer evidence from which we can draw a definitive conclusion.
Competing Interests: Nil
1. Fleming PJ, Blair PS, Ward Platt M, Tripp J, Smith IJ, Golding J,
the CESDI SUDI research group. The UK accelerated immunisation programme
and sudden unexpected death in infancy: case control study. BMJ
2. Willinger M. Sleep position and sudden infant death syndrome. JAMA
1995 March 8th; 273(10): 818-9.
3. Klonoff-Cohen HS, Edelstein SL.. A case-control study of routine
and death scene sleep position and sudden infant death syndrome in
Southern California. JAMA 1995 March 8th; 273(10): 790-794.
4. Wisborg K, Kesmodel U, Henriksen TB, Olsen SF, Secher NJ. A
prospective study of smoking during pregnancy and SIDS. Arch Dis Child
5. Ford RP, Taylor BJ, Mitchell EA, Enright SA, Stewart AW, Becroft
DM, Scragg R, Hassall IB, Barry DM, Allen EM, Roberts AP. Breastfeeding
and the risk of sudden infant death syndrome. Int J Epidemiol 1993
Competing interests: No competing interests