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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