China discovers new flu virus, has the potential to become a pandemic

Research in China has provided new evidence that the world may be on the brink of another pandemic as cases of bird flu have emerged in several areas in poultry, livestock and humans.

Avian influenza A viruses are divided into subtypes based on the combination of two proteins found on their surface – hemagglutinin and neuraminidase – known as HxNy.

According to the Centers for Disease Control and Prevention (CDC) in the United States, only two subtypes of avian influenza A – H1N1 and H3N2 – are known to circulate in humans.

A study led by China's top virologist has raised concerns that a new strain of H2N2 virus discovered in nature could now infect humans, raising the need for closer surveillance.

Many different strains of the virus have been found in birds and other animal populations around the world, some of which can infect humans.

George Fu Gao, an immunologist who served as director of the Chinese Center for Disease Control and Prevention from 2017 to 2022, published a paper with his team at the Chinese Academy of Sciences investigating the specific H2N2 strain of the virus.

Decades ago, another strain of H2N2 caused the 'Asian flu' pandemic , which broke out in 1957 in southern China and quickly spread around the world, killing more than 1 million people, according to the CDC.

Following the pandemic, H2N2 became a seasonal influenza and eventually disappeared from human populations by the late 1960s, although low-virulence strains continued to circulate in Chinese poultry.

In a paper published in the peer-reviewed journal Nature Communications on November 19, Gao and his team said that after testing several H2N2 strains, one strain from 2021 was able to bind to both bird and human receptors on the surface of host cells.

While this H2N2 strain still preferred the bird receptor, the authors say the virus that caused Asian flu also initially preferred dual receptors, but over time became more adapted to the human receptor.

The team's experiments in mice, guinea pigs and ferrets showed that the H2N2 strain can rapidly adapt to mice and acquire mammalian-adaptive mutations that help it spread to guinea pigs and ferrets, the preferred animal models for influenza.

The researchers also examined the impact of individual mutations on the transmissibility and virulence of the 2021 H2N2 strain and found that some mutations may change their binding preference to human receptors.

Despite similarities between the recent H2N2 strain and the one that caused the 1957 pandemic, the team said genetic differences and the length of time since the Asian flu outbreak leave the world with no immunity to a future outbreak.

There are similarities between the recent H2N2 strain and the strain that caused the 1957 pandemic.

The disease risk of H2N2 remains low and there is only limited transmission between mammals, reducing the overall risk of a pandemic from circulating H2N2 strains, the researchers said.

'However, the H2N2 [low pathogenic avian influenza] strain has recently acquired limited mutations that increase its virulence in mice and allow transmission between mammals ,' the team said.

One of the most famous variants of avian influenza A is H1N1 – also known as swine flu – which caused the first flu pandemic of the 21st century in 2009.

A common strain of avian influenza – H5N1 – has made headlines due to outbreaks on dairy farms in the United States, leading to more than 40 human infections in the United States this year, according to the CDC.

Most cases have been linked to contact with cattle or poultry, and none of the recent cases have been caused by human-to-human transmission, but experts say the possibility remains.

Of the more than 900 cases of H5N1 infection confirmed and reported to the World Health Organization between 2003 and 2024, about half resulted in death.

Outbreaks in farm animals are particularly worrying because viruses can undergo reassortment, or swapping genome segments between viruses. When avian influenza viruses enter pigs – which can carry both human and avian diseases – the risk of reassortment with seasonal human influenza increases.

Another paper published in the journal Nature Microbiology on Monday by a team of researchers from the United States and the Netherlands indicates that H5N1 could pose a much greater pandemic risk.

In a brief article, the scientists said they began studying H5N1 because of a " recently detected abrupt change" in the virus, characterized by an ongoing outbreak in dairy cattle in the United States.

Researchers examined viral shedding — the process of expelling virus particles through processes such as exhalation — of the new H5N1 strains compared with older strains in ferrets.

The team found that compared with the H5N1 virus from the 2000s, the recent viruses had "low but increasing" levels of airborne virus shedding , which may explain the recent increase in transmission between cattle.

'Strengthening surveillance of [avian influenza viruses] in animals and assessing the public health risks of novel [avian influenza viruses] is imperative to control and prevent emerging and re-emerging influenza pandemics and epidemics,' the Chinese research team said .