Table 4.

 Summary of crude and adjusted results in subgroups defined by exposure status or baseline risk of events

	No (%) exposed*	No (%) non-exposed†	Event prevalence ratio (crude) (95% CI)	Adjusted odds ratio (95% CI)
Exposure
Per protocol	7293 (23.9)	23 195 (76.1)	0.76 (0.69 to 0.83)	0.80 (0.72 to 0.89)
Alternative analysis 1*	11 565 (38.6)	18 382 (61.4)	0.79 (0.74 to 0.85)	0.83 (0.76 to 0.91)
Alternative analysis 2†	7293 (28.0)	18 795 (72.0)	0.74 (0.67 to 0.81)	0.77 (0.68 to 0.86)
Subgroup analysis
Prenatal control <4	976 (13.4)	6319 (86.6)	0.73 (0.61 to 0.89)	0.76 (0.58 to 0.97)
Prenatal control ≥4	6325 (27.3)	16 876 (72.7)	0.88 (0.79 to 0.98)	0.84 (0.73 to 0.95)
High risk fifth	1234 (21.1)	4605 (78.9)	0.72 (0.62 to 0.83)	0.62 (0.52 to 0.75)
Low risk	6010 (24.6)	18 454 (75.4)	0.84 (0.74 to 0.94)	0.87 (0.77 to 0.99)

*Women with documented H1N1 vaccine plus those who reported having received H1N1 monovalent vaccine but for whom no official record or documentation was available versus non-vaccinated women.

†Women with vaccine documentation versus non-vaccinated women, excluding those whose vaccination status was only self reported.