The UK accelerated immunisation programme and sudden unexpected death in infancy: case-control study

Objectives To investigate whether the accelerated immunisation programme in the United Kingdom is associated after adjustment for potential confoundin g, with the sudden infant death syndrome. Design Population based case-control study; February 1993 to March 1996. Pa rental interviews were conducted for each death and for four controls match ed fur age, locality; and time of sleep, Immunisation status was taken from records held by the parents. Setting Five regions in England with a combined population of over 17 milli on, Subjects Immunisation details were available for 93% (303/325) of infants w hose deaths were attributed to the sudden infant death syndrome (SIDS): 90% (65/72) of infants with explained sudden deaths; and 95%, (1515//1588) of controls. Results After alt potential confounding factors were controlled for, immuni sation uptake was strongly associated with a lower risk of SIDS (odds ratio 0.45 (95% confidence interval 0.24 to 0.85), This difference became non-si gnificant (0.67; (0.31 to 1.43)) after further adjustment for other factors specific to the infant's sleeping environment. Similar proportions of SIDS deaths and reference sleeps (corresponding to the time of day during which the index baby had died) among the controls occurred within 48 hours of th e last vaccination (5% (7/149) v 5% (41/822)) and within two weeks (21% (31 /149) v 27% (224/822)). No longer term temporal association with immunisati on was found (P = 0.78). Of the SIDS infants who died within two weeks of v accination, 16% (5/31) had signs and symptoms of illness that suggested tha t medical contact was required, compared with 26% (16/61) of the non-immuni sed SIDS infants of similar age. The findings for the infants who died sudd enly and unexpectedly but of explained causes mirrored those for SIDS infan ts. Conclusions Immunisation does not lead to sudden unexpected death in infanc y, and the direction of the relation is towards protection rather than risk .