Table 3. Influenza Vaccine Effectiveness by Control Group and Vaccine Type.

		Cases	Controls	Crude odds ratio	Adjusted odds	Vaccine Effectiveness
		n (%)	n (%)	(95% CI)	ratio (95% CI)*	(95% CI)
Healthy controls (matched) *
Vaccinated (any vaccine)
Yes		458 (80.2)	1903 (83.3)	0.81 (0.53–0.96)	0.84 (0.55–1.01)	16% (−1 to 45)
No		113 (19.8)	381 (16.7)	Ref	Ref	Ref
Vaccinated (TIV)
Yes		151 (57.2)	687 (64.3)	0.74 (0.56–0.97)	0.77 (0.58–1.01)	23% (−1 to 42)
No		113 (42.8)	381 (35.7)	Ref	Ref	Ref
Vaccinated (LAIV)
Yes		301 (72.7)	1163 (75.3)	0.87 (0.68–1.11)	0.89 (0.69–1.15)	11% (−15 to 31)
No		113 (27.3)	381 (24.7)	Ref	Ref	Ref
Test-negative controls (unmatched)^
Vaccinated (any vaccine)
Yes		485 (80.4)	308 (69.7)	1.79 (1.34–2.38)	0.71 (0.47–1.06)	29% (−6 to 53)
No		118 (19.6)	134 (30.3)	Ref	Ref	Ref
Vaccinated (TIV)
Yes		170 (59.0)	168 (55.6)	1.15 (0.83–1.59)	0.47 (0.29–0.75)	53% (25 to 71)
No		118 (41.0)	134 (44.4)	Ref	Ref	Ref
Vaccinated (LAIV)
Yes		307 (72.2)	139 (50.9)	2.51 (1.82–3.45)	1.13 (0.73–1.77)	−13% (−77 to 27)
No		118 (27.8)	134 (49.1)	Ref	Ref	Ref

^*Adjusted for sex, age group, and number of prior vaccinations.

^Adjusted for sex, age group, number of prior vaccinations, and month of diagnosis.