The rapidly evolving H5N1 virus has prompted the World Health Organization (WHO) to initiate pre-pandemic vaccine development.

Since the 1990s, bird flu has caused over 860 human infections globally, with a mortality rate exceeding 50%. First identified in humans in 1997, H5N1 predominantly affects birds but has occasionally infected humans through direct exposure. Although the virus hasn't demonstrated human-to-human transmission, its recent spread to mammals has raised concerns about its potential adaptation.

In response, the WHO is working on vaccines using H5N1 strains detected in the US and South America, aiming for swift deployment if needed.

Recent Developments and Risks
The latest outbreak began in 2021 when migratory birds carried the clade 2.3.4.4b strain to North America. By 2022, it led to a mink farm outbreak in Spain, which was contained through culling. Over the past ten months, North America has recorded 68 human cases, including one fatality.

Although most human cases have been mild, scientists warn that each spillover into mammals increases the risk of mutations that could enable human-to-human transmission. Alarmingly, at least 40 cases of infection linked to dairy cows have been reported in the US.

Dr Joseph Sriyal Malik Peiris of the University of Hong Kong highlights the importance of vigilance, warning that sustained transmission in mammals could heighten risks for humans.

Protective Measures
While the risk to humans remains low, experts stress the need for precautions, especially for workers in high-risk environments.

Dr Peiris advises US dairy workers to use personal protective equipment, as infected cows can carry high viral loads in milk. He also warns against consuming raw milk, emphasising that pasteurisation kills the virus and ensures safe consumption.

Beyond dairy, the public is urged to avoid contact with sick or dead wild birds and stranded marine mammals, as these may carry the virus.

Though H5N1 hasn't reached pandemic levels, continued surveillance, early precautions, and vaccine readiness are vital to preventing a potential health crisis.