JAMA Netw Open

Second flu shot boosts effectiveness in youngest vaccine-naive children

October 7, 2025

Study details: This systematic review and meta-analysis evaluated the added protection of a second influenza vaccine dose in vaccine-naive children aged 6 months to under 9 years. Researchers screened MEDLINE, EMBASE, and CINAHL through March 2025, identifying 51 peer-reviewed studies with over 415,000 participants.

Results: Among children younger than 3 years, a second dose of inactivated influenza vaccine increased effectiveness by 28 percentage points (95% confidence interval [CI], 4.7–51 pp). For children under 9 years, the increase was 15 pp (95% CI, –2.8 to 33 pp), which wasn't statistically significant. Data were insufficient to assess the benefit of a second dose of live attenuated influenza vaccine.

Clinical impact: The findings support the two-dose schedule for vaccine-naive children under 3, consistent with WHO guidance. For older children, the benefit is unclear, highlighting the need for age-specific recommendations and further high-quality studies.

Source:

Goldsmith JJ, et al. (2025, October). JAMA Netw Open. Comparison of 2 Doses vs 1 Dose in the First Season Children Are Vaccinated Against Influenza: A Systematic Review and Meta-Analysis. https://pubmed.ncbi.nlm.nih.gov/41042511/