Table 2.

Comparison of vaccine effectiveness (VE) by vaccination group and influenza type/subtype

VE comparison	Relevance of results	H1N1	H3N2	B
Vaccinated both seasons versus vaccinated prior season only ΔVEa (95% CI) ΔVE = VEboth – VEprior only	Patient and policy perspectives	26% (15% to 36%)	10% (–6% to 25%)	24% (7% to 42%)
Vaccinated current season only versus vaccinated neither season (reference group) Pooled VEcurrent only	Patient and policy perspectives	61% (50% to 70%)	41% (33% to 48%)	62% (54% to 68%)
Vaccinated both seasons versus vaccinated current season only ΔVEa (95% CI) ΔVE = VEboth – VEcurrent only	Policy perspective	4% (–7% to 15%)	–12% (–27% to 4%)	–8% (–17% to 1%)

Bold type-face indicates significant results

^aΔVE > 0 implies higher vaccine effectiveness estimate when vaccinated in both seasons