Table 4. Influenza Vaccine Effectiveness by Influenza Subtype: Comparison to Matched Healthy Controls.

Influenza Subtype	Vaccinated	Cases	Controls	Odds ratio	Vaccine Effectiveness
		n (%)	n (%)	(95% CI)	(95% CI)
Influenza A/H1 (pandemic)
	Yes	53 (86.9)	202 (82.8)	1.38 (0.61–3.11)	−38% (−211 to 39)
	No	8 (13.1)	42 (17.2)	Ref	Ref
Influenza A/H3
	Yes	59 (76.6)	273 (88.6)	0.42 (0.22–0.79)	58% (21 to 78)
	No	18 (23.4)	35 (11.4)	Ref	Ref
Influenza B
	Yes	29 (87.9)	121 (91.7)	0.66 (0.20–2.22)	34% (−122 to 80)
	No	4 (12.1)	11 (8.3)	Ref	Ref

^*Influenza subtype data only available for USAFSAM cases. Due to small sample size, adjusted estimates not available.