Recombinant Flu Shots Extend Protection to Children
METHODOLOGY:
Researchers conducted a phase 3, non-randomised, immunobridging study during the 2022-2023 northern hemisphere influenza season to evaluate whether immune responses to RIV4 in children (aged 9-17 years) were non-inferior to those in adults (aged 18-49 years).
They enrolled 648 children and adolescents (mean age, 13 years; 52% boys) and 660 adults (mean age, 34.3 years; 40% men).
All participants received a single intramuscular dose of RIV4 (45 μg haemagglutinin of each of A/H1N1, A/H3N2, B/Victoria, and B/Yamagata strains) and were monitored for 6 months on days 9, 29, and 181.
The endpoint was measured using haemagglutination inhibition (HAI) titre ratios and the difference in seroconversion rates at day 29 post-vaccination.
Non-inferiority was established if the lower limit of the 95% CI exceeded 0.667 for geometric mean titre ratios and −10% or above for seroconversion, for each of the four strains.
TAKEAWAY:
At day 29, the ratio of geometric mean HAI titres between children and adolescents and adult groups was well above the prespecified non-inferiority margin for A/H1N1 (2.0; 95% CI, 1.7-2.3), H3N2 (3.3; 95% CI, 2.8-3.9), B/Victoria (1.6; 95% CI, 1.4-1.8), and B/Yamagata (1.2; 95% CI, 1.1-1.4) strains.
Similarly, the difference in seroconversion rates between the two groups was also above the prespecified non-inferiority margin for all the four strains.
The safety profile of RIV4 was comparable between the two groups; however, solicited reactions within 7 days post-vaccination were less common in children and adolescents than in adults.
None of the serious and medically attended adverse events were related to the vaccine, and no deaths or adverse events of special interest were reported in either group.
IN PRACTICE:
"Having multiple influenza vaccine options is crucial to successfully combating influenza, and these options need to be available for children. Prioritising children in influenza vaccine studies is an important step in combating the global burden of influenza," the authors of a commentary wrote.
SOURCE:
This study was led by Pedro M. Folegatti, DPhil, Sanofi, Marcy-l'Étoile, France. It was published online on May 21, 2025, in The Lancet Infectious Diseases .
LIMITATIONS:
This study did not investigate immune responses in children younger than 9 years. The evaluation was limited to just one influenza season, and no clinical testing for influenza disease or infection was conducted, potentially accounting for some of the increased antibody responses observed.
DISCLOSURES:
This study was funded by Sanofi. Seven authors reported being employees of and may have held shares in Sanofi. Two other authors reported having financial ties with other pharmaceutical companies.
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