Synthesizing and assessing influenza vaccine evidence: Strengths and limitations of the recent ECDC report on the effectiveness of new and enhanced influenza vaccines. Communication on: the "European Centre for Disease Prevention and Control. Systematic review update on the efficacy, effectiveness and safety of newer and enhanced seasonal influenza vaccines for the prevention of laboratory confirmed influenza in individuals aged 18 years and over. Stockholm: ECDC; 2024".

High quality research is critical for evidence-based decision making in public health and fundamental to maintain progress and trust in immunization programs in Europe. In 2024 the European Centre for Disease Prevention and Control (ECDC) conducted an update of the 2020 systematic review to capture more recent evidence on of the efficacy, effectiveness of influenza vaccines in individuals aged 18 years and older in the prevention of laboratory-confirmed influenza. While this report was highly anticipated due to the strength of the protocol and processes put in place, during our assessment, we expressed two chief concerns. We are concerned by the grading of the evidence certainty applied and being unable to reproduce some data extracted in the report from the primary sources. While the systematic review benefited of strong methods and processes, the execution of the research protocol warrants revision due to the issues discussed. We encourage the ECDC to work towards an updated review within a reasonable time frame to avoid misinterpretation by decision-making bodies across Europe.