Two mathematical models published by PAIR explore complementary strategies for High Pathogenic Avian Influenza (HPAI) preparedness

Highly pathogenic avian influenza viruses continue to circulate among wild birds and domestic poultry, occasionally infecting mammals and humans. Although current human cases are generally associated with exposure to infected animals rather than sustained transmission between people, the continued evolution and geographical spread of these viruses make them an important focus for pandemic preparedness.
Preparing for a possible future outbreak requires understanding two connected challenges. The first is how infection moves between wild birds, poultry and humans, and which animal-health measures could reduce spillover. The second is how a hypothetical human outbreak might develop if efficient human-to-human transmission emerged, particularly when vaccines are not immediately available or accepted by everyone.

Two PAIR-funded publications from UGA research foundation, address these questions through complementary mathematical models. These studies do not report the observed effectiveness of interventions during an actual human HPAI epidemic. Instead, they use defined assumptions and simulations to compare possible transmission patterns and control strategies.

Modelling highlights the importance of coordinated action and early intervention

The first study developed a phylogeny-informed model linking wild birds, domestic poultry and humans. Genetic evidence was used to support the transmission pathways represented in the model, while simulations assessed interventions across the different host populations. Under the scenarios examined, vaccination with sufficiently high efficacy and coverage reduced transmission indicators and modelled human infections. Reducing contact between birds and people also lowered estimated spillover risk. Among the combinations evaluated, environmental sanitation together with targeted poultry culling produced the largest modelled reduction in transmission.

The second study considered a hypothetical outbreak within a human population. Its model explicitly represented the incubation period, the delay before vaccination could begin and the time required for vaccinated individuals to develop protection. It also distinguished between vaccine-accepting and vaccine-hesitant groups and examined adherence to non-pharmaceutical interventions.
The simulations indicated that delays in vaccine deployment or immune protection could substantially reduce vaccination’s ability to limit the early epidemic peak. Earlier deployment and higher acceptance were associated with lower peak and cumulative infections. Non-pharmaceutical measures reduced transmission immediately and were therefore most influential during the early phase, although their effects depended on sustained compliance.
Both these models support preparedness strategies that connect animal and human health, reduce opportunities for spillover and plan for the period before vaccines become widely available and effective.

• Read and download the phylogeny-informed HPAI H5N1 modelling paper.
• Read and download the time-delayed vaccination and intervention modelling paper.