Interim influenza vaccine effectiveness estimates during the 2023 Southern Hemisphere season

Our findings suggest that a substantial number of people sought care for CLI during an early Southern Hemisphere season during which A/H1N1pdm09 clade 6B.1A.5a.2a viruses predominated. The minority vaccinated benefitted from the A/Victoria/2570/2019 (H1N1)pdm09-like antigen which afforded good protection against illness. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was supported by the Centers for Disease Control and Prevention cooperative agreement award GH00266. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was approved by the institutional review board of Universidad Peruana Cayetano (PRISA repository: EI0002439) Centers for Disease Control and Prevention non-research determination 0900f3eb81ecbe9f. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors.