Table 2.

Effect of influenza vaccination status in the current and 5 prior seasons in preventing laboratory-confirmed influenza among patients with chronic obstructive pulmonary disease.

	Cases/controls	Vaccination effect, (95% CI)a	p value
All patients
Never vaccinated	154/215	Reference
Vaccination in prior seasons only	79/172	24 (–10 to 47)	0.146
Current season vaccination	309/832	40 (20 to 54)	< 0.001
Aged 25–64 years
Never vaccinated	80/90	Reference
Vaccination in prior seasons only	25/45	–2 (–98 to 48)	0.965
Current season vaccination	38/126	56 (24 to 74)	0.003
Aged ≥ 65 years
Never vaccinated	74/125	Reference
Vaccination in prior seasons only	54/127	28 (–13 to 55)	0.150
Current season vaccination	271/706	33 (6 to 52)	0.019
Male
Never vaccinated	96/142	Reference
Vaccination in prior seasons only	50/116	26 (–18 to 53)	0.212
Current season vaccination	216/619	36 (8 to 55)	0.014
Female
Never vaccinated	58/73	Reference
Vaccination in prior seasons only	29/56	25 (–41 to 60)	0.375
Current season vaccination	93/213	43 (7 to 64)	0.023
Primary healthcare patients
Never vaccinated	54/30	Reference
Vaccination in prior seasons only	5/7	58 (–85 to 92)	0.252
Current season vaccination	33/35	60 (–5 to 85)	0.061
Hospital patients
Never vaccinated	100/185	Reference
Vaccination in prior seasons only	74/165	19 (–19 to 45)	0.285
Current season vaccination	276/797	37 (15 to 53)	0.002

CI confidence interval.

^aVaccination effect adjusted by age groups (25–64, 65–84 and ≥ 85 years), other major chronic conditions, healthcare setting (primary healthcare or hospital), and month-season of sample collection.