constant protection regardless of the severity of the disease

Influenza vaccination demonstrates consistent effectiveness of approximately 50% across all severity levels in children, with higher protection observed in younger children (aged 6 months to 8 years) than in older children. (ages 9 to 17). The study was carried out by the Dre Kelsey M. Sumner of National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention (Atlanta, United States). It was published online on December 27, 2024 in JAMA Network Open.

Methodology

• Researchers conducted a negative case-control study to evaluate vaccine effectiveness (VE) against severe influenza in children across eight pediatric medical centers in the United States between November 2015 and April 2020.

• A total of 15,728 children (44.6% girls) who were hospitalized or presented to an emergency department (ED) for acute respiratory illness at participating hospitals were included. Among them, 85.5% were aged 6 months to 8 years and the remaining 14.5% were aged 9 to 17 years.

• Overall, 13,018 children tested negative for influenza, while the remaining 2,710 children tested positive for influenza. The severity of the flu was classified into three categories: those who had to go to the emergency room (61.8%), those who had to be hospitalized for non-critical flu (33.1%), and those who had to be hospitalized for critical influenza (5.1%).

• Children aged ≥9 years were classified as vaccinated if they had received at least one dose of the current season’s influenza vaccine at least 14 days before symptom onset.

• VE was calculated based on influenza severity and status

Main results

Overall, 49.5% of children were vaccinated, with the majority (87.3%) aged 6 months to 8 years. Unvaccinated children were hospitalized longer and spent more days in the intensive care unit than vaccinated children, if hospitalized.

The overall VE after receiving at least one dose of influenza vaccine was 55.7% [51,6–59,6 %] and was higher among children aged 6 months to 8 years than among those aged 9 to 17 years (58.1% versus 42,6 %).

VE remained constant across all severity levels: 52.8% for illness requiring an emergency room visit, 52.3% for non-critical illness requiring hospitalization, and 50.4% for serious illness requiring hospitalization .

“Vaccination is one of the most effective ways to protect children against influenza and its complications, including severe illness and hospitalization. Improving vaccination coverage among children could reduce the risk of influenza illness and, subsequently, emergency room and hospital visits in the context of increased co-circulation of the respiratory virus,” the authors write.

Limitations of the study

The requirement for written informed consent led to the non-inclusion of many children, particularly those in critical condition. The flu may not have been as severe as it appeared, as only two deaths were reported during the five years of the study. Other limitations included the limited inclusion of patients not attending the emergency department, as well as the lack of generalizability of the results to a broader population.

This article was translated from the American edition of Medscape.com part of the Medscape professional network, using several editorial tools, including AI, in the process. The content was reviewed by the editorial staff before publication.