Table 4.

Mean logarithmic titre changes in the vaccine group for smoker compared with non-smoker

Strain	Smoking category	Pre-titre	Post-titre	Mean titre change	Difference in mean titre change (95% CI)a	Adjusted difference in mean titre change (95% CI)a,b
Change post-titre–pre-titre (151 smokers, 580 non-smokers)
AS	smoker	0.80	1.92	+1.12	0.20 (0.07–0.34)	0.18 (0.04–0.32)
	non-smoker	0.78	1.70	+0.92
AB	smoker	0.88	2.31	+1.43	0.03 (−0.11–0.17)	0.05 (−0.09–0.20)
	non-smoker	0.86	2.26	+1.40
BP	smoker	1.25	2.57	+1.32	0.02 (−0.08–0.13)	0.03 (−0.07–0.14)
	non-smoker	1.16	2.46	+1.30
BB	smoker	1.19	2.54	+1.35	0.12 (0.02–0.23)	0.12 (0.00–0.25)
	non-smoker	1.19	2.42	+1.23
Change end-titre–post-titre (146 smokers, 544 non-smokers)c
AS	smoker	1.96	1.70	−0.26	−0.04 (−0.10–0.02)	−0.05 (−0.11–0.01)
	non-smoker	1.72	1.50	−0.22
AB	smoker	2.35	1.98	−0.37	−0.05 (−0.11–0.00)	−0.05 (−0.11–0.01)
	non-smoker	2.31	1.99	−0.32
BP	smoker	2.57	2.36	−0.21	−0.02 (−0.06–0.03)	−0.02 (−0.07–0.03)
	non-smoker	2.47	2.28	−0.19
BB	smoker	2.53	2.23	−0.30	−0.03 (−0.08–0.02)	−0.05 (−0.10–0.00)
	non-smoker	2.42	2.15	−0.27

AS, A/Singapore/6/86 (H1N1); AB, A/Beijing/353/89 (H3N2); BP, B/Panama/45/90; BB, B/Beijing/11/87.

Geometric mean titre (GMT)=10^logtitre: change(GMT)=10^{logchangevalue}∗10^logprevalue−10^logprevalue.

^aCI indicates confidence interval.

^bCorrected for age, sex and risk group, but not for protective titre before vaccination (possible intermediate factor).

^cSubjects with serological influenza were excluded (=a titre at end-titre ≥4 times the titre at post-titre) causing a small difference to occur in the post-titre used in post-titre–pre-titre compared to the post-titre used in end-titre–post-titre.