Scientists in China have identified a new strain of flu that has the potential to become a pandemic. The sceintists say it has come to light recently and is carried by pigs, but can infect humans.
There is concern among researchers that there could be further mutations so that it can spread easily from person to person, and trigger a worldwide outbreak. While it is not an immediate problem, they say, it has "all the hallmarks" of being highly adapted to infect humans and needs to be monitored closely.
The scientists write in the journal Proceedings of the National Academy of Sciences that measures to control the virus in pigs, and the close monitoring of swine industry workers, should be swiftly implemented.
A bad new strain of influenza is among the top disease threats that experts are on the look out for even as the world tries to put an end to the COVID-19 pandemic.
The last pandemic flu the world dealt with was the swine flu outbreak of 2009 - was less deadly than initially feared, largely because many older people had some immunity to it, probably because of its similarity to other flu viruses that had circulated years before.
That virus, called A/H1N1pdm09, is now covered by the annual flu vaccine to make sure people are protected. The new flu strain that has been identified in China is similar to 2009 swine flu, but with some modifications.
So far, it hasn't posed a big threat, but Prof Kin-Chow Chang and colleagues who have been studying it, say it is one to keep an eye on.
The big question how concerned should we be?
The virus, which the researchers call G4 EA H1N1, can grow and multiply in the cells that line the human airways. They found evidence of recent infection in people who worked in the pig industry in China when they looked at data from 2011 to 2018.
Current flu vaccines do not appear to protect against it, although they could be adapted to do so if needed.
Prof Kin-Chow Chang, who works at Nottingham University in the UK and told media "Right now we are distracted with coronavirus and rightly so. But we must not lose sight of potentially dangerous new viruses." While this new virus is not an immediate problem, he says: "We should not ignore it."
In theory, a flu pandemic can happen at any time, but they are still rare occurances. Pandemics happen if a new strain emerges that can easily spread from person to person. Although flu viruses are constantly changing - which is why the flu vaccine also needs to change regularly to keep up - they do not usually go pandemic.
A World Health Organization spokeswoman said: "Eurasian avian-like swine influenza virus are known to be circulating in the swine population in Asia and to be able to infect humans sporadically.
Twice a year during the influenza vaccine composition meetings, all information on the viruses is reviewed and the need for new candidate vaccine viruses is discussed.