Bird flu, especially the rapidly spreading H5N1 strain, is being closely watched by scientists over the years, not because it is spreading widely in humans yet, but because of how close it may be to doing so. H5N1 isn’t known to easily infect people.
According to Nature Spotlight: Influenza, H5N1 currently doesn’t bind well with cell receptors in the upper airway of people but in 2024, scientists said it could as a single mutation would enable H5N1 to readily attach to human lung cells. Once the virus can replicate in the lung, it would gain the ability to transmit through the air, potentially triggering a large outbreak. Scientists also warn that most people have little to no immunity against H5N1, meaning even a modestly lethal version could have severe global consequences.
According to WHO, from 2003 to August 2025, 990 human H5N1 cases have been reported across 25 countries, which includes 475 deaths. Symptoms in humans includes high fever, cough, sore throat, muscle aches, and conjunctivitis.
While humans transmission cases of bird flu are extremely low, scientists want to understand how a bird flu pandemic if it ever happens in humans could play out.
A new model published in the BMC Public Health journal led by Indian researchers Philip Cherian and Gautam Menon of Ashoka University, through real world data and computer simulations demonstrate what will happen if a bird flu outbreak happens in real life, and what early interventions can be taken to stop it from spreading.
How a bird flu pandemic could begin
Researchers say the bird flu pandemic may begin with a single infected bird passing on the infection to a human – who would more likely be a farmer, market worker or poulterer. However, that infection alone wouldn’t trigger a pandemic, but what would happen next – a sustained human-to-human transmission.
The researchers presented their an open-source simulation platform originally built for Covid 19 modelling. The paper would help policymakers to take appropriate action before an outbreak spirals out of control.
The study estimates that once the cases spike 2 to 10, the disease may spread beyond primary and secondary contacts – meaning those who have direct contact with the infected person and those who are close with the primary contact but not met the infected person.
How bird flu can be contained
Quarantining households of primary contacts when just two cases are detected could contain the outbreak most certainly. However, if the step if taken at the time of 10 cases, it’s likely the infection has already spread to a larger population, says the research.
How the research was conducted
To reflect real-world risk as closely as possible, the researchers built a detailed computer simulation based on a single village in Namakkal district of Tamil Nadu – the region chosen due to its importance in India’s poultry economy.
Using publicly available demographic and occupational data, the researchers created a synthetic community of 9,667 residents, complete with households, schools, workplaces, farms and market spaces, mirroring everyday movement and contact patterns.
The simulation was seeded with infected birds at one workplace, such as a mid-sized poultry farm or wet market, to replicate a likely spillover scenario.
The model tracked how the virus first spread to primary human contacts at the site of exposure and then moved through fixed social networks like homes, schools and workplaces and to secondary and tertiary contacts.
The researchers estimated key outbreak parameters such as the basic reproductive number (R₀) across a range of plausible transmission rates, and then tested how different interventions like bird culling, isolation, household quarantine and targeted vaccination altered the course of a potential outbreak.