Australia: A systematic review and meta-analysis found that two doses of inactivated influenza vaccine provided better protection than a single dose in influenza vaccine–naive children younger than 3 years. However, the additional benefit diminished with age and was not statistically significant when children younger than 9 years were considered. Further high-quality studies are needed to determine the age groups that benefit most from a two-dose vaccination schedule.

The study, published in JAMA Network Open, was conducted by Jessie J. Goldsmith, MSc, from the Department of Infectious Diseases at the University of Melbourne, Peter Doherty Institute for Infection and Immunity, Melbourne, Australia, and colleagues.
The World Health Organization (WHO) recommends that children younger than 9 years who have never received an influenza vaccine receive two doses during their first vaccination season, based on evidence from immunogenicity studies. However, the extent to which the second dose improves actual protection against influenza remains uncertain.
To investigate this, the researchers evaluated the additional protection associated with a second influenza vaccine dose in children aged 6 months to younger than 9 years who had no previous influenza vaccination. They searched MEDLINE, EMBASE and CINAHL for relevant peer-reviewed studies published up to March 24, 2025.
The review included studies reporting vaccine efficacy or effectiveness according to the number of doses received. Two reviewers independently screened the studies, extracted data, and assessed the risk of bias. The analysis included 51 studies involving 415,050 participants. The researchers compared vaccine efficacy or effectiveness after one and two doses, examining inactivated influenza vaccines (IIV) and live attenuated influenza vaccines (LAIV) separately.
The analysis revealed the following findings:
  • Among children younger than 9 years, receiving a second dose of IIV was associated with an estimated 15-percentage-point increase in vaccine effectiveness. However, the confidence interval ranged from a decrease of 2.8 percentage points to an increase of 33 percentage points, indicating that the difference was not statistically significant.
  • In children younger than 3 years, the second IIV dose was associated with a 28-percentage-point increase in vaccine effectiveness, with a 95% confidence interval ranging from 4.7 to 51 percentage points. This improvement was statistically significant.
  • The additional protection associated with the second dose appeared to diminish with increasing age, although insufficient data were available to establish the benefit specifically among children aged 3 to younger than 9 years.
  • The researchers could not reliably estimate the additional protection provided by a second LAIV dose because too few suitable estimates were available.
The findings suggest that a second dose of inactivated influenza vaccine offers additional protection to vaccine-naive children younger than 3 years, but the benefit was not statistically significant in children younger than 9 years.
The study was limited by few available estimates, small sample sizes, and potential bias in observational studies. The researchers called for high-quality trials and observational studies to determine the benefits of a two-dose schedule across age groups.
Reference:
Goldsmith JJ, Tavlian S, Vu C, et al. Comparison of 2 Doses vs 1 Dose in the First Season Children Are Vaccinated Against Influenza: A Systematic Review and Meta-Analysis. JAMA Netw Open. 2025;8(10):e2535250. doi:10.1001/jamanetworkopen.2025.35250
Tags:    
Article Source : JAMA Network Open

Disclaimer: This website is primarily for healthcare professionals. The content here does not replace medical advice and should not be used as medical, diagnostic, endorsement, treatment, or prescription advice. Medical science evolves rapidly, and we strive to keep our information current. If you find any discrepancies, please contact us at corrections@medicaldialogues.in. Read our Correction Policy here. Nothing here should be used as a substitute for medical advice, diagnosis, or treatment. We do not endorse any healthcare advice that contradicts a physician's guidance. Use of this site is subject to our Terms of Use, Privacy Policy, and Advertisement Policy. For more details, read our Full Disclaimer here.

NOTE: Join us in combating medical misinformation. If you encounter a questionable health, medical, or medical education claim, email us at factcheck@medicaldialogues.in for evaluation.

Medha Baranwal

Medha Baranwal holds a Bachelor’s degree in Biomedical Sciences from the University of Delhi and a Master’s degree in Biotechnology from Amity University. Since May 2018, she has been contributing to Medical Dialogues, writing and editing medical news articles that translate complex research into clear, accessible information for healthcare professionals.

Comments Policy
Our comments section is governed by our Comments Policy . By posting comments at Medical Dialogues you automatically agree with our Comments Policy , Terms And Conditions and Privacy Policy .