Evaluating the Incremental Benefit of Two Versus One Dose of Influenza Vaccine in Influenza-Naive Children Under Nine: A Systematic Review and Meta-Analysis

Highlight

• WHO recommends two influenza vaccine doses for vaccine-naive children under 9 based on immunogenicity evidence.
• The meta-analysis shows a 28 percentage point increase in vaccine effectiveness with two doses in children under 3 years old.
• For children under 9, the additional protection from a second inactivated vaccine dose was 15 percentage points but did not reach statistical significance.
• There is insufficient evidence on incremental benefits of second doses for live attenuated influenza vaccines, indicating a need for further high-quality studies.

Study Background and Disease Burden