The Avian Influenza Matching (AIM) Project
OFFLU AIM technical report (September 2025)
Link to report: OFFLU AIM Technical Report (September 2025)
About OFFLU
OFFLU is an open, global network dedicated to advancing knowledge and strengthening preparedness and response to animal influenza across regions, institutions, and areas of expertise.
The WOAH/FAO International Reference Laboratory for Avian Influenza (IRL) at APHA is a key member of OFFLU. This is a collaborative network of international expertise on animal influenzas, established by the FAO and WOAH. The ethos behind OFFLU uses a One Health approach, aiming to address the veterinary and zoonotic threat of animal influenza viruses through surveillance, prevention and disease control projects.
The growing challenge of HPAIV
Since 2020, high pathogenicity avian influenza viruses (HPAIV) of clade 2.3.4.4b have shifted from being a seasonal concern to a persisting, dominating global threat, leading to unprecedented poultry outbreaks and severe measurable economic burdens.
In addition, epizootic and zoonotic concerns have intensified due to recent HPAIV spillover events and infection of mammals. To combat the growing threat, FAO/WOAH support and recommend vaccination for the control and prevention of HPAI in certain contexts. Therefore, up-to-date characterisation of virus glycoprotein evolution is a crucial activity to understand the impacts of changing viral evolutionary dynamics on vaccine coverage.
The Avian Influenza Matching (AIM) Project
Annually, the IRL leads the Avian Influenza Matching (AIM) project, providing real-time, objective information on the protection elicited by antigenic candidates from current poultry vaccines against contemporary circulating H5Nx strains of the A/Goose/Guandong/1986 lineage.
The AIM project 2025 involved a collaborative network of WOAH/FAO International Laboratories (APHA, UK; IZSVe, Italy; CSIRO ACDP, Australia and USDA SEPRL, USA), testing their repositories of historic and contemporary H5Nx influenza strains, including representatives from the globally dominant clade 2.3.4.4b and geographically restricted East Asian clades 2.3.2.1a/e/g and 2.3.4.4h.
Report
Study design and methodology
In September the latest collaborative technical report was released. The project workflow employed haemagglutination inhibition assays, testing a total of 88 H5Nx viruses spanning 2016 to 2025, against chicken antisera generated from antigens representative of vaccine seed strains.
Antigenic cartography and visualisation
Results are visualised through antigenic cartography (Figure 1), which illustrates the antigenic distance between field viruses and the seed strains used to generate vaccines.
Link to report: OFFLU AIM Technical Report (September 2025)
Figure 1. Three-dimensional antigenic map illustrating the relationship among H5Nx A/Goose/Guandong/1986 lineage avian influenza viruses characterised in this study. Each sphere represents a test virus, coloured by subtype and clade. Squares represent post-vaccination chicken antisera generated from vaccine strains. (Modified: OFFLU, 2025).
Key findings on vaccine matching
Results indicated that H5N8 clade 2.3.4.4b antigens remain suitable candidates for inactivated whole-virus adjuvanted vaccines for most contemporary 2024-2025, 2.3.4.4b H5Nx viruses. Findings also highlighted the potential importance of clade specific vaccination approaches as vaccine antigens from heterologous clades, including ancestral strains, demonstrated limited serological cross-reactivity against contemporary H5Nx 2.3.4.4b viruses.
Evidence of regional viruses variation
Critically, the study highlighted the importance of continual characterisation and surveillance of region specific H5Nx viruses. Regional viruses such as the contemporary 2024 South Asian H5N1 clade 2.3.2.1a virus demonstrated limited cross-neutralisation against heterologous antisera.
Further, clade 2.3.2.1a isolates from 2021 to 2024 exhibited decreasing levels of neutralisation by ancestral clade 2.3.2.1 antisera, suggesting antigenic drift and accumulated evolutionary distance over time.
Summary
Looking ahead
This OFFLU funded project is extended through 2026 and into 2027, continuing to update antigenic maps and evaluate antigenic distance between novel global influenza isolates.
Global collaboration
Such analyses are only possible through the global support of a broad range of countries who we thank for their participation in sharing material for analysis:
Europe:
Belgium
Bulgaria
Croatia
Czech Republic
Finland
Croatia
Georgia
Ireland
Italy
Kosovo
Latvia
Moldova
Norway
Poland
Romania
Slovakia
Slovenia
Spain
Switzerland
Ukraine
Africa
Benin
Burkina Faso
Cambodia
Cameroon
Ghana
Guinea
Ivory Coast
Niger
Nigeria
Togo
Australia, Bangladesh, Canada, Falkland Islands, Republic of Indonesia, Iran, Israel, Ivory Coast, Nepal, Philippines, Saint Helena, Ascension and Tristan da Cunha, South Georgia and the South Sandwich Islands, Turkey, and Viet Nam.