Controlling for individual potential confounders of immunisation

Potential confounders Proportion (%) of immunised infants
Mantel-Haenszel pooled odds ratio (95% confidence interval)

SIDS infants Control infants

Overall 149/303 (49) 822/1234 (67) 0.48 (0.37 to 0.63)^*

Age of infant (days):

  <91 33/157 (21) 184/546 (34)

  91-120 36/46 (78) 177/200 (89)

  >120 80/100 (80) 461/488 (94) 0.43 (0.29 to 0.59)

Socioeconomic group:

  I and II 18/43 (42) 280/428 (65)

  III (non-manual) 44/78 (56) 266/387 (69)

  III (manual) and IV 60/114 (53) 215/328 (66)

  V and unemployed 27/67 (40)   58/87 (67) 0.50 (0.38 to 0.65)

Moved house in past year:

  No 82/159 (52) 651/977 (67)

  Once 47/94 (50) 139/204 (68)

  Twice or more 20/49 (41)   30/50 (60) 0.51 (0.38 to 0.66)

Maternal age (years):

  >29 29/62 (47) 271/410 (66)

  25-29 30/75 (40) 305/444 (69)

  <25 90/166 (54) 246/380 (65) 0.49 (0.37 to 0.63)

No of children in family:

  1 child 47/84 (56) 354/529 (67)

  2 or 3 children 80/169 (47) 414/610 (68)

  >3 children 22/50 (44)   54/95 (57) 0.50 (0.39 to 0.66)

Birth weight (g):

   $>=$ 2500 116/236 (49) 776/1163 (67)

  <2500 33/67 (49)   39/64 (61) 0.50 (0.38 to 0.66)

Gestational age (weeks):

  >38 49/104 (47) 453/696 (65)

  37-38 70/140 (50) 319/461 (69)

  <37 30/58 (52)   41/66 (62) 0.48 (0.37 to 0.63)

Admitted to special care baby unit:

  No 112/229 (49) 751/1139 (66)

  Yes 37/74 (50)   65/87 (75) 0.47 (0.35 to 0.61)

Admitted to hospital:

  No 97/212 (46) 664/1027 (65)

  Yes 51/88 (58) 157/206 (76) 0.45 (0.35 to 0.59)

Five minute Apgar score:

   $>=$ 8 139/277 (50) 772/1170 (66)

  <8 6/15 (40)   20/25 (80) 0.50 (0.38 to 0.65)

Apparent life threatening event^§:

  No episodes 128/262 (49) 792/1196 (66)

  One episode or more 19/34 (56)   29/37 (78) 0.48 (0.36 to 0.62)

SIDS infants=infants whose deaths were attributed to sudden infant death syndrome.

^* Unmatched odds ratio.

Cut-offs were chosen on the basis of the infants who died within three months (some of who died after vaccination at age 2 months), those who died aged 3 to 4 months (after the second vaccination), and those who died after age 4 months and the final vaccination.

Based on highest occupational status of parent(s) and previous occupation if currently unemployed.

^§ Any episode of lifelessness described by the parents.