Table 3.

Multivariable Regression: Association of frailty (ref = non-frail) to 2013–2014 vaccine strains stratified by age group (adjusted for BMI and baseline log₂ titers)

	< 65 years (N = 66)			≥ 65 years (N = 40)
Variable (frail vs. non-frail)	Odds Ratio	95% Confidence Interval	P value	Odds Ratio	95% Confidence Interval	P value	P value for age difference
Seroprotection at Day 21a
H1N1 A/California/07/2009	8.79	1.78 – 43.31	0.008**	0.54	0.12 – 2.52	0.43	0.009*
H3N2 A/Texas/50/2012	6.00	1.25 – 28.75	0.02*	0.36	0.06 – 1.99	0.23	0.014*
B/Massachusetts/2/2012	7.79	1.15 – 52.61	0.03*	0.46	0.05 – 4.67	0.51	0.05
Seroconversionb
H1N1 A/California/07/2009	6.86	1.55 – 30.37	0.011*	0.75	0.17 – 3.30	0.70	0.045*
H3N2 A/Texas/50/2012	5.85	1.86 – 18.40	0.003**	0.29	0.05 – 1.73	0.17	0.005**
B/Massachusetts/2/2012	2.68	0.81 – 8.78	0.107	0.61	0.14 – 2.68	0.51	0.221
Log2 D21 HAI antibody titersc
H1N1 A/California/07/2009	0.55	0.15	<0.001**	0.06	0.25	0.82	0.06
H3N2 A/Texas/50/2012	0.50	0.17	0.005**	−0.26	0.17	0.15	0.002**
B/Massachusetts/2/2012	0.29	0.14	0.05	−0.17	0.14	0.23	0.04*

^*significant at P value <0.05

^**significant after adjusting for multiple comparisons 0.05/6, P value 0.0083

^aLogistic Regression: Event sizes for Seroprotecting at Day 21: H1N1 (N = 38 <65 years; N = 22 ≥65 years); H3N2: (N = 48 <65 years; N = 21 ≥65 years); B: (N = 51 <65 years; N = 29 ≥65 years)

^bLogistic Regression: Event sizes for Seroconverting: H1N1 (N = 13 <65 years; N = 11 ≥65 years); H3N2: (N = 25 <65 years; N = 9 ≥65 years); B: (N = 19 <65 years; N = 12 ≥65 years)

^cLinear regression equation: Log₂ D21 HAI titer = B₀ + B_1*Frail + B_2*BMI + B_{3*log2 baseline titer} +E