Table 2. Comparison of antibody responses against influenza vaccine strains among the study participants (N = 132).

Antibody response*	Pregnant women (n = 66)		p-value† (Pregnancy)	Non-Pregnant women (n = 66)		p-value‡ (Interaction)
	Vaccinated with IIV3			Vaccinated with IIV3
	Yes (n = 33)	No (n = 33)		Yes (n = 33)	No (n = 33)
Influenza A/Michigan/45/2015 (H1N1)pdm09
Pre-vaccine GMT (Day 0)	16.5	15.6	0.704	18.4	16.2	0.677
Post-vaccine GMT (Day 28)	171.8	14.6	<0.001	106.1	17.0	0.089
GMR (Fold increase after 28 days)	20.9	0.3	<0.001	14.9	1.5	0.219
Seroconversion (%)	88.8	2.9	<0.001	62.5	2.9	0.797
Seroprotection (%) (Day 0)	21.3	23.4	0.899	28.0	21.2	0.490
Seroprotection (%) (Day 28)	88.2	23.0	<0.001	78.7	22.2	0.517
Influenza A/Singapore/INFIMH-16-0019/2016 (H3N2)
Pre-vaccine GMT (Day 0)	26.6	24.6	0.534	29.4	25.3	0.673
Post-vaccine GMT (Day 28)	195.7	26.7	<0.001	241.1	27.5	0.653
GMR (Fold increase after 28 days)	26.4	0.4	<0.001	21.2	0.3	0.611
Seroconversion (%)	69.5	8.4	<0.001	76.0	5.8	0.630
Seroprotection (%) (Day 0)	46.9	37.9	0.455	48.6	42.4	0.850
Seroprotection (%) (Day 28)	91.7	44.6	<0.001	92.6	43.8	0.896
Influenza B/Phuket/3073/2013
Pre-vaccine GMT (Day 0)	13.6	13.2	0.677	13.3	13.3	0.758
Post-vaccine GMT (Day 28)	94.7	12.2	<0.001	113.5	13.1	0.720
GMR (Fold increase after 28 days)	12.3	<0.1	<0.001	21.1	0.5	0.133
Seroconversion (%)	76.9	0	<0.001	76.7	2.9	0.993
Seroprotection (%) (Day 0)	8.9	12.1	0.655	9.0	9.4	0.661
Seroprotection (%) (Day 28)	88.1	7.7	<0.001	82.0	10.0	0.434

Abbreviations: IIV3, trivalent inactivated influenza vaccine; GMT, Geometric mean titer; GMR, Geometric mean titer ratio.

*Estimates of antibody response and p-values derived from multilevel regression analyses after controlling for baseline antibody titer and prior influenza vaccination.

p-value^† (pregnancy); comparing vaccinated and non-vaccinated participants within pregnant group.

p-value^‡ (interaction); comparing effect of vaccination across pregnant and non-pregnant participants.