How Much Of A Risk Is Bird Flu? Study Raises Fears For Humans

A bird flu virus spreading widely among U.S. cattle only needs to change slightly to potentially pass between humans, scientists have found.

Researchers probing an H5N1 virus passed from a cow to a human have shown a single mutation could make it much better at latching on to people.

This mutation has not been found in nature and academics say there are several further barriers to person-to-person transmission.

Nonetheless, the Science study highlights the risks posed to humans by the ongoing bird flu outbreak.

So far, 58 people in the U.S. have caught the disease, which is widespread among birds and has infected cows in several states. Almost all human cases have been linked to contact with animals.

Most infections have been mild, but some, like the case of a Canadian teenager who was hospitalized in November, have caused severe illness.

Should We Be Worried About Bird Flu?

Some governments are already stocking up on H5 vaccines just in case it develops the ability to pass between people. These would provide protection against the symptoms of the disease and potentially slow its spread.

Before COVID-19, many countries saw flu as the most likely candidate for a future pandemic. Resilience plans and preparedness stockpiles were tailored to the disease.

It’s not hard to see why. Humans have endured at least 14 flu pandemics since 1500, five of which took place in the last 140 years. The most recent struck just 15 years ago — 2009’s swine flu pandemic.

These large outbreaks occur after spillover events, when a type of flu passes from animals to humans, then learns how to spread between people. The transmissability and severity of each specific flu will vary, and can change over time as a virus spreads.

The Great Flu Pandemic from 1918 and 1920 saw at least a third of the world’s population infected with H1N1 flu. Some estimates put the infection rates at 56% of the population, or even higher. Nobody knows exactly how many people it killed, but it’s thought to have taked between 17 million and 100 million lives.

Most flu pandemics since then have been smaller. But they’ve still killed hundreds of thousands of people, and put serious pressure on healthcare systems which already face millions of seasonal flu cases every year.

Why Can’t Bird Flu Spread Between People?

Right now, the strain of flu spreading between birds and cows (H5N1) has not evolved to pass between humans.

That’s because it’s not particularly good at infecting our upper respiratory tract — the nose, mouth, sinuses, throat and voicebox.

But that could change if the virus adapts in the right way.

Viruses spread by replicating themselves, sometimes imperfectly. This leads to small alterations or “mutations,” some of which can change the way a virus spreads.

At the moment, there are “many barriers” to bird flu adapting well enough to pass between humans, says Ed Hutchinson, professor of molecular and cellular virology at the Medical Research Council-University of Glasgow Centre for Virus Research.

“The most important [barrier] is probably the ability of the virus to bind to new cells by grabbing onto sugars on the cell surface with ‘spikes’ of a protein called HA,” he told the Science Media Centre. “These sugars are different shapes in different animals. Birds make different sugars from humans.”

The Science study looked at the HA protein of a virus that had passed from a cow to a human in Texas.

As the sugars on cow cells resemble those of birds more closely than those of humans, the virus would still needs to adapt its HA protein to get better at infecting people.

The research shows this could happen — in principle, at least — with just a single mutation.

Is Bird Flu Likely To Spread Between People In Future?

The mutation in question has not been observed in nature, and may never occur in the real world.

Even if it did, that doesn’t mean it would have the effect scientists anticipate. As professor David Heymann from the London School of Hygiene and Tropical Medicine says: it’s “impossible to predict how this [mutation] may change the behaviour of the organism in humans.”

There are also a number of other barriers facing the virus, according to Prof Hutchinson. Other properties of the HA protein would need to change for the virus to be able spread by aerosols — tiny, infected airborne particles.

“We also do not know for sure if this mutation has any hidden costs for the virus which might make it harder to acquire,” he added.

That being said, the mutation is still a serious concern for scientists and lawmakers. Influenza can mutate very quickly compared to lots of other viruses.

Hutchinson said the study underlines the importance of watching the virus as closely as possible and preparing in case it does learn how to spread between people.

We need to take “the current outbreak in cattle in the USA… extremely seriously,” he said. “Every effort” needs to made to watch how the virus evolves and to “intervene where possible to limit its opportunities to try out its options of evolving further in humans.”