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Table 2 Comparison of vaccine effectiveness (VE) by vaccination group and influenza type/subtype

From: The impact of repeated vaccination on influenza vaccine effectiveness: a systematic review and meta-analysis

Vaccine effectiveness 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 25% (14%, 35%) 7% (− 7%, 21%) 18% (3%, 33%)
Vaccinated current season only versus vaccinated neither season (reference group) Pooled VEcurrent only Patient and policy perspectives 62% (51%, 70%) 45% (35%, 53%) 64% (57%, 71%)
Vaccinated both seasons versus vaccinated current season only ΔVEa (95% CI) ΔVE = VEboth – VEcurrent only Policy perspective 3% (− 8%, 13%) – 20% (− 36%, − 4%) – 11% (− 20%, − 2%)
  1. Italic type-face indicates significant results
  2. aΔVE > 0 implies higher vaccine effectiveness estimate when vaccinated in both seasons