Table 2:

Influenza-related acute respiratory infection in the overall groups and COPD severity subgroups in patients with and without influenza vaccination (N=320).

	Acute respiratory infection	p-value‡	Incidence	RD	RR	Effectiveness [1-RR]×100 (%)
	Yes n (%)†	No n (%)†
Overall
Vaccine	76 (47.5)	84 (52.5)	0.176	0.48	0.08	1.19	N/A
No vaccine	64 (40.0)	96 (60.0)		0.40
Subgroups:
Low severity*
Vaccine	6 (15.0)	34 (85.0)	0.062	0.15	- 0.15	0.50	50
No vaccine	36 (30.0)	84 (70.0)		0.30
High severity*
Vaccine	70 (58.3)	50 (41.7)	0.190	0.58	- 0.12	0.83	17
No vaccine	28 (70.0)	12 (30.0)		0.70
M-H adjusted RR						0.73	27
M-H test of homogeneity (p-value)						0.169
Magnitude of confounding (%)**						63.0

RD, risk difference; RR, risk ratio; N/A, not applicable

M-H adjusted RR, Mantel-Haenszel adjusted RR

M-H test of homogeneity, Mantel-Haenszel test of homogeneity of stratum-specific RRs

^†Percentage by row

^‡Chi-square test

*Severity of COPD

**Calculated by [(RRcrude – RRadjusted) / RRadjusted]×100%.