A large European primary care study found that the flu vaccine provided strong protection to children over two seasons, with clear benefits against influenza B and H1N1.
Study: Effectiveness of influenza vaccine in European primary care pediatric practices: 2022-2024. Image Credit: Art_Photo/Shutterstock
A recent study published in the journal Pediatrics Shows that influenza vaccines provide strong real-world protection for children across Europe against influenza in primary care settings. Vaccine Effectiveness (V.E) depending on virus subtype, was between 57-83% in 2022-2023 and increased to 71-92% in 2023-2024.
Overall, at least 65% of children vaccinated in both seasons were protected, underscoring the consistent benefits of vaccination against influenza in primary care settings. The findings highlight the importance of pediatric vaccination and the need to scale it up while continuing to monitor effectiveness to guide vaccination strategies.
The burden of childhood influenza and gaps in vaccine evidence.
Children suffer a heavy burden from seasonal influenza, resulting in more frequent primary care visits and missed school days each year. However, real-world vaccine effectiveness in pediatric primary care across Europe remains limited.
EU countries (European Union) and the European Economic Area (EEA) prioritize influenza vaccination for high-risk children, and some even make recommendations for all children. Despite this, data on vaccine effectiveness across age groups, vaccine types and seasons remains scarce.
This difference matters because dosing schedules vary by age and prior vaccination, and vaccine formulations are updated annually. Addressing these limitations is key to improving safety and guiding more effective, evidence-based vaccination strategies.
Pediatric Influenza Vaccine Study Design
In the current study, researchers assessed influenza vaccine effectiveness (V.E) among children attending primary care centers European Union And EEA During 2022-2023 and next year. he analyzed V.E Based on virus subtype, age group and vaccination target status using a test-negative case-control design at 10 study sites in nine countries.
General practitioners collected nasopharyngeal or oropharyngeal swabs and saliva samples at a pediatric site from children with symptoms of acute respiratory tract infection (ARI). These include cough, sore throat, cold or difficulty in breathing. Samples were obtained within eight days of symptom onset. The team performed real-time polymerase chain reaction (PCR) to confirm influenza infection, with further virus subtyping in regional or national laboratories. PCR-Positive children represented cases, while children who tested negative served as controls.
The team collected clinical and demographic data through interviews and medical records, including age, gender, co-morbidities, symptom onset and vaccination status. They confirmed vaccination status through electronic health records, national registries, or patient/parent report. Only those people who had received the vaccine at least two weeks before the onset of symptoms were considered vaccinated in the study.
Researchers used logistic regression models adjusted for major confounders to estimate V.E To examine differences against all influenza viruses and by subtype. He also compared V.E In children aged 0-8 and 9-17 years. Additionally, the investigators conducted a sensitivity analysis excluding children younger than one year of age to account for vaccine eligibility limitations.
Vaccine effectiveness results by season and age
The study included 10,368 primary care recipients during 2022-2023, 32% of whom were tested PCR-Positive. In 2023–2024, positivity dropped to 17% among 9,270 children, apparently reflecting low positivity rates in the study sample rather than a direct measure of incidence. Circulating strains also changed: influenza A H3N2 and influenza B viruses were dominant in 2022–2023, while influenza A H1N1 dominated the next season. The proportion of children in the vaccination target group among controls increased from 17% to 38% over the two sessions.
Overall vaccine effectiveness (V.E) stay strong. In 2022-2023, V.E Reached 68% against all influenza viruses, including 57% against H1N1, 54% against H3N2 and 83% against influenza B. Over the next year, overall V.E This increased to 71%, with 75% protection against H1N1 and 92% protection against influenza B virus, however. V.E Compared to H3N2, it reduced to 40%.
Age-specific analyzes revealed differences. In 2022-2023, V.E Children aged 0–8 years had more protection against H1N1 (70%) and influenza B (86%) than older children, while children aged 9–17 years showed stronger protection against H3N2 (63%). In 2023-2024, younger children again perform better V.E against H1N1 (78%), while protection against influenza A H3N2 remained modest in both age groups. Sensitivity analysis excluding children under one year of age resulted in minimal change (<5.0%) V.E The estimates support the robustness of the findings.
Pediatric Influenza Vaccination Implications
Study findings show that influenza vaccination provided consistent and meaningful protection among children across two seasons in Europe. V.E Estimates show that more than two-thirds of vaccinated children included in primary care were protected against influenza in both seasons. Protection was strongest against influenza B and H1N1, but was lower and more variable for H3N2, likely reflecting factors such as antigenic drift, vaccine match, and viral evolution. Vaccine effectiveness also varies by age, with younger children generally having higher protection.
The results highlight the importance of improving vaccination coverage, particularly within recommended target groups, to maximize direct benefits and reduce the overall burden of seasonal influenza.
Continued monitoring of vaccine effectiveness in pediatric populations is essential to track age- and subtype-specific trends, inform timely vaccine updates, and support decisions on expansion of vaccination strategies to better protect both high-risk and healthy children. However, the authors also note limitations, including incomplete data on dosing history and vaccine type, which may affect interpretation of some subgroup findings. The 92% projection for influenza B in 2023–2024 should also be interpreted with caution as it was based on only three study sites.
