Healthy adults possess cross-reactive neuraminidase inhibition antibodies to an A(H5N1) clade 2.3.4.4b avian influenza virus A/Black Faced Spoonbill/Hong Kong/AFCD-HKU-22-21429-01012/2022

Hemagglutination inhibition (HI) and neuraminidase inhibition (NI) antibodies to a clade 2.3.4.4b A(H5N1) highly pathogenic avian influenza virus were measured in 63 age-stratified healthy adults in Hong Kong. No HI antibody was detected; 61 subjects had detectable NI antibodies to A(H5N1). NI titers to A(H5N1) and A(H1N1)pdm09 viruses were correlated. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was funded by RGC Theme-based Research Schemes (T11-712/19-N), Hong Kong SAR, China. ### 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: IRB of the University of Hong Kong/Hospital Authority Hong Kong West Cluster gave human ethics approval for this work (#UW-132) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the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