FRIDAY, October 17, 2025 (News) — Getting two doses of inactivated flu vaccine (IIV) during a child’s first year of vaccination offers better protection for those under 3 years old compared to just one dose, as found in a study released online on October 3 inJAMA Network Open.
Jessie J. Goldsmith, affiliated with the University of Melbourne in Australia, along with her team, performed a comprehensive analysis of existing research to determine the enhanced protection provided by the second dose of the flu vaccine among children under 9 years old who had not previously received the vaccine.
From 51 studies involving 415,050 individuals, the researchers discovered that the combined absolute rise in vaccine efficiency from a second inactivated influenza vaccine dose during the initial year of vaccination was 15 percentage points (pp) among those under 9 years old (95 percent confidence interval [CI], −2.8 pp to 33 pp) and 28 pp (95 percent CI, 4.7 pp to 51 pp) for children under 3 years. The additional advantage of a second dose of live attenuated influenza vaccine could not be evaluated.
“Our results indicate that the second dose of an inactivated flu vaccine provides extra protection for children under three years old who have not received the vaccine before, although this advantage decreases as they grow older,” the authors state.
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