Flu vaccines protect children well across Europe, but H3N2 remains harder to stop

By Pooja Toshniwal PahariaReviewed by Susha Cheriyedath, M.Sc.Apr 8 2026

A large European primary care study found that flu vaccines provided children with strong protection over two seasons, with the clearest benefits against influenza B and H1N1.

Study: Influenza Vaccine Effectiveness 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 provided strong real-world protection in children across Europe against primary care-attended influenza. Vaccine effectiveness (VE) ranged from 57–83% in 2022–2023 and rose to 71–92% in 2023–2024, depending on the virus subtype.

Overall, at least 65% of vaccinated children were protected in both seasons, underscoring the consistent benefits of vaccination against influenza in primary care settings. The findings highlight the value of pediatric vaccination and the need to increase uptake while continuing to monitor effectiveness to guide immunization strategies.

Childhood Influenza Burden and Vaccine Evidence Gaps

Children bear a heavy burden of seasonal influenza, resulting in frequent primary care visits and missed school days each year. However, real-world vaccine effectiveness in pediatric primary care across Europe remains limited.

Countries in the European Union (EU) and European Economic Area (EEA) prioritize influenza vaccination for high-risk children, and some also extend recommendations to all children. Despite this, data on vaccine effectiveness across age groups, vaccine types, and seasons remain scarce.

This gap matters because dosing schedules vary by age and prior vaccination, and vaccine formulations are updated annually. Addressing these limitations is key to improving protection and guiding more effective, evidence-based immunization strategies.

Pediatric Influenza Vaccine Study Design

In the present study, researchers assessed influenza vaccine effectiveness (VE) among children visiting primary care centers across the EU and EEA during 2022–2023 and the following year. They analyzed VE by virus subtype, age group, and vaccination target status using a test-negative case-control design across 10 study sites in nine countries.

General practitioners collected nasopharyngeal or oropharyngeal swabs and saliva samples at one pediatric site from children presenting with symptoms of acute respiratory tract infections (ARI). These included cough, sore throat, coryza, or shortness of breath. The 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 those testing negative served as controls.

The team gathered clinical and demographic data through interviews and medical records, including age, sex, comorbidities, symptom onset, and vaccination status. They confirmed vaccination status through electronic health records, national registries, or patient/guardian reports. The study considered only those who received vaccines at least two weeks before symptom onset as vaccinated.

The researchers used logistic regression models adjusted for key confounders to estimate VE against all influenza viruses and to examine differences by subtype. They also compared VE in children aged 0–8 and 9–17 years. Furthermore, the investigators conducted a sensitivity analysis excluding children under one year to account for vaccine eligibility limitations.

Vaccine Effectiveness Results by Season and Age

The study included 10,368 primary care recipients during 2022–2023, of whom 32% tested PCR-positive. In 2023–2024, positivity dropped to 17% among 9,270 children, reflecting a markedly lower positivity rate in the study sample rather than a direct measure of incidence. Circulating strains also shifted: influenza A H3N2 and influenza B viruses were predominant in 2022–2023, while influenza A H1N1 dominated in the following season. The proportion of children in the vaccination target group among controls rose from 17% to 38% across the two seasons.

Overall vaccine effectiveness (VE) remained strong. In 2022–2023, VE against all influenza viruses reached 68%, including 57% against H1N1, 54% against H3N2, and 83% against influenza B. In the following year, the overall VE increased to 71%, with 75% protection against H1N1 and 92% against influenza B virus, although VE against H3N2 declined to 40%.

Age-specific analyses revealed variation. In 2022–2023, VE among children aged 0–8 years was higher for H1N1 (70%) and influenza B (86%) compared to older children, while those aged 9–17 years showed stronger protection against H3N2 (63%). In 2023–2024, younger children again showed higher VE against H1N1 (78%), whereas protection against influenza A H3N2 remained modest across both age groups. Sensitivity analyses excluding children under one year resulted in minimal changes (<5.0%) to VE estimates, supporting the robustness of the findings.

Pediatric Influenza Vaccination Implications

The study findings show that influenza vaccination provided consistent and meaningful protection among children in Europe over two seasons, with VE estimates indicating that more than two-thirds of vaccinated children were protected against primary care-attended influenza in both seasons. Protection was strongest against influenza B and H1N1, but remained lower and more variable for H3N2, possibly reflecting factors such as antigenic drift, vaccine match, and viral evolution. Vaccine effectiveness also differed by age, with generally higher protection in younger children.

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 expanding immunization strategies to better protect both high-risk and healthy children. However, the authors also note limitations, including incomplete data on dose history and vaccine type, which may affect the interpretation of some subgroup findings. The 92% estimate for influenza B in 2023–2024 should also be interpreted cautiously because it was based on only three study sites.