Table 3 Effectiveness of prophylaxis: cases of VKDB grouped by treatment intended, from the second and third surveys*.

Prophylaxis intended	Estimated§ at‐risk population‡	Cases of VKDB	Estimated§ incidence	Relative risk versus IM (95% CI)
Intramuscular	1575 000†	11	1 in 143 000	1
Oral beyond a week	928 000†	11	1 in 84 400	1.70 (0.74 to 3.91), p = NS
Oral not beyond a week	371 000	10	1 in 37 100	3.86 (1.64 to 9.09), p<0.02
Nil	32 000	2	1 in 16 000	8.95 (1.98 to 43.4), p<0.01
Overall	3 066 000	34	1 in 90 200

*Surveys of incidence 1993–94 and 2001–02; five cases excluded as details of intended prophylaxis were not available. The first incidence survey, 1998–90, did not include the question “What was unit policy for this infant?”.

†Populations offered a choice between IM and oral are allocated equally between groups.

‡Population includes all infants (all gestations, birth weights, risk categories, etc).

§Estimated because firm data were unavailable as some babies were given different prophylaxis from that routinely recommended for normal risk deliveries, either through parental choice or clinician allocation.