Are we playing chicken with bird flu?

By Professor Stuart Berzins

As attention to COVID-19 wanes, the World Health Organization warns that bird flu could become the next global pandemic. These warnings are not new, as the WHO and other public health groups have been concerned about bird flu since well before COVID-19 arrived, but why the increased concern now?

What is bird flu?

Influenza viruses are categorised into Types A, B and C, but there are many subvariants within these groups that differ in how they are transmitted and their disease severity.

Bird flu refers to a subtype of influenza A viruses called H5N1 that are endemic to many wild bird populations and causes wasting, poor egg production and often the eventual death of the bird. Outbreaks of H5N1 in commercial settings (e.g., egg or meat production) pose a threat to entire industries and usually result in entire flocks being euthanised, which can mean killing millions of birds and the shutdown of farms.

Apart from the economic impact, scientists are concerned that variants of H5N1 will develop that infect other animals. This would present a significant health threat because humans are not usually infected by the H5N1 virus, and as such, our immune protection against what would be a new threat is expected to be very poor.

Indeed, while there have been fewer than 1,000 confirmed cases of people contracting H5N1 influenza, more than half of those infected have died, so the prospect of this disease gaining a COVID-like transmissibility is extremely worrying.

Is the threat growing?

There is currently a large bird flu outbreak across dozens of countries where hundreds of millions of birds have died or been euthanised. High numbers of infections increase the likelihood of harmful mutations, and this appears to have happened already because bird-to-animal transmission of H5N1 has now resulted in the death of bears, raccoons and foxes.

Most of these deaths probably resulted from animals eating infected birds, but there have also been outbreaks where entire mink farms and seal colonies have become infected. These are unlikely to have been due solely to contact with infected birds, so it now appears that a variant has emerged that can be transmitted between non-avian species, including mink, pigs and seals, which have very similar respiratory systems to humans.

Fortunately, very few humans have contracted the virus, but the extent of these outbreaks increases the potential for mutations that allow H5N1 to infect humans.

What should we look out for?

A worrying progression would be to see transmission from infected animals to humans, and worse still would be transmission from human to human – particularly if transmission was airborne as it is for COVID-19.

Thankfully, the current variants of H5N1 don’t seem to easily infect humans, but the unprecedented size and spread of the latest outbreak creates a genetic lottery where more infectious mutations of one virus could easily arise or where viruses ‘swap’ genetic material to produce a hybrid with traits of both parental strains.

For example, the Omicron variants BA.2.10.1 and BA.2.75 combined to produce the XBB 1.5 variant that dominates many current COVID-19 outbreaks. Therefore, if someone (e.g., poultry farm workers) became co-infected with the H5N1 virus while also carrying a human influenza virus, a far more infectious variant of H5N1 could emerge.

In a worrying sign, a genetic mutation known to promote mammalian virus transmission was recently found in an H5N1 outbreak spreading throughout mink farms in Denmark.

Should we be worried?

The flip side to these concerns is that we can take easy steps to avoid, or at least minimise, the chance of an H5N1 pandemic. Firstly, the virus is mostly transmitted through faeces or body fluids from an infected bird, so the likelihood of a mutation leading to airborne transmission between humans is thought to be low.

It is also reassuring that, despite close contact with farmed animals, there have been fewer than 1,000 worldwide cases of bird flu in humans in decades of monitoring the virus, with most of those resulting from animal-to-human (not human-to-human) transmission after prolonged exposure to infected animals, e.g., farmers.

There are straightforward precautions to reduce the risks even further. For example, better segregation of farmed and wild animals (many mink farms are open-air buildings that wild birds can enter) should reduce H5N1 spread between species. Effective vaccines have also been developed against H5N1 that are not widely used but could be used to protect vulnerable species (e.g., mink, poultry, pigs) and farm workers from cross-infection.

The stockpiles of the human vaccine are worryingly low, and the current manufacturing capacity is estimated at 150 million in 6 months, which is not sufficient for a global population of 7 billion. COVID showed the importance of rapid, worldwide vaccine distribution, so we should build this stockpile and develop new vaccines. RNA vaccine platforms that proved so important for COVID-19 prevention would be useful because current influenza vaccines are grown in hen eggs, thus creating a potential problem if bird flu infects the vaccine egg-production flock.

Action needed

Bird flu presents a real risk to humans, and we should act now to improve farm management, increase surveillance of virus infections and fund the development of new treatments and vaccines that we might need sooner than we hope.

Many of these are lessons learned during the COVID-19 pandemic, so hopefully, our fatigue with that pandemic doesn’t prevent us from properly preparing for the next one.

Stuart Berzins is Professor of Immunology at Federation University.