Comparison of 2 Doses vs 1 Dose in the First Season Children Are Vaccinated Against Influenza A: A Systematic Review and Meta-Analysis

Submitted by: Inês Barreira do Couto, Jorge Rodrigues, ULS Viseu Dão Lafões, Viseu, PortugalBackground: Background: Every year, about 20% of children contract influenza, which significantly increases pediatric morbidity and mortality. Children under five years old are disproportionately involved in community transmission and have the highest hospitalization rates linked to influenza. Influenza vaccine (IV)-naive children under nine years old should receive two doses during their first vaccination season, according to WHO. This recommendation is based on immunogenicity research showing that adults need two doses to reach protective seropositivity thresholds. However, there is little evidence to support the clinical benefit of this approach, and it is still unclear whether these thresholds apply to children. This systematic review assessed whether the suggested two-dose priming schedule is supported by the available IV efficacy and effectiveness studies for IV-naive children between the ages of six months and nine years.Main Findings: This analysis included 51 studies with a total of 415 050 children. The pooled absolute increase in vaccine effectiveness for the inactivated IV following a second dose was 15 percentage points (pp) (95% CI –2.8-33) for children under the age of nine and 28 pp (95% CI 4.7-51) for children under the age of three. There was not enough data to assess the incremental benefit of live-attenuated vaccines.Take home message: There is still little clinical evidence to support the two-dose priming schedule recommended by guidelines. The inactivated IV is recommended for children under three years old because a second dose appears to provide more protection, but it is unclear if a second dose would be beneficial for older kids.