A group of scientists have created a simulation to show how bird flu could spill over to humans if the correct vaccination and confinement measures are not taken.

Researchers have widely warned of a possible future pandemic caused by what they called “Disease X”– an infection that originates in animals and later jumps to humans.

A candidate for such a disease is highly pathogenic avian influenza (HPAI), commonly called bird flu, as experts from the World Health Organization (WHO) have warned.

The research, conducted by Ashoka University and published in BMC Public Health examines how quickly an outbreak might escalate once human-to-human transmission begins.

So far, there have not been reports of these happening, according to the European Centre for Disease Prevention and Control (ECDC).

The health agency said in its latest report this month that the magnitude and geographical extent of these detections were unprecedented for this time of the year, particularly in wild birds.

Avian influenza has been spreading at elevated levels worldwide over the past five years, including in wild and farm birds in the European Union. In recent years, it has also spread to mink, cats, a captive bear, and other mammals, raising the risk that the virus will eventually reach people.

The simulation recreates a small village in the state of Tamil Nadu in southern India – a region that houses more than 1,600 poultry farms that rear over 70 million chickens.

Scientists started with a small number of infected birds and no infected humans. They recreated an outbreak at a poultry farm where they show two scenarios: when infected birds are rapidly contained, no human is infected; however, if there is no culling or it comes too late, several workers get infected.

In many scenarios of the simulation, nothing happens – the virus never reaches people, especially when infected birds are killed early, so the flock is removed before infections peak and the risk to humans falls to zero.

But in others, one or two farm workers after a three-day latent period become Infectious for about seven days, heading home each evening to infect household members.

The simulation shows that there is a small window, between about two and 10 detected cases, when control is still possible before the virus escapes into the wider community.

If at the start of the infections, households are quarantined, the virus is likely to be contained.

However, if the number of cases reaches 10, the simulations show that some infected household members have already gone to their workplaces and schools, passing the virus to others.

By this point, it has entered the wider population and created new, independent chains of transmission that quarantining the original households can no longer fully stop.

Mathematically, when quarantine is delayed to 10 cases, the estimated reproductive ratio and epidemic curves look very similar to the “no early intervention” scenario, because much of the onward spread has already occurred.

With the findings, researchers highlight the need to act before community transmission happens – after that, only broad tools such as lockdowns and mass vaccination remain effective.

The simulation has some limitations, mainly that it does not include multiple simultaneous outbreak sites, behavioural change such as personal protective equipment use after bird outbreaks are noticed, or intermediate mammal hosts.