A new strain of swine flu that has the potential to cause another pandemic has been labelled "very, very dangerous" and a "salutary reminder" that humans are constantly at risk of new diseases jumping the species barriers from animals.
However, Chinese media have played down concerns with warnings not to "overreact". That's despite the new strain being found in pigs in China.
Yesterday it was revealed Chinese researchers had found a new and concerning strain of swine flu.
Named genotype 4, or G4, it is genetically descended from the H1N1 swine flu strain that caused a pandemic in 2009.
It possesses "all the essential hallmarks of being highly adapted to infect humans," said scientists at Chinese universities and China's Centre for Disease Control and Prevention.
Over a period of seven years, researchers took thousands of swabs from pigs in slaughterhouses in Chinese provinces and a veterinary hospital, allowing them to isolate 179 swine flu viruses.
The majority were of a new kind which has been dominant among pigs since 2016.
The G4 virus was observed to be highly infectious, replicating in human cells and causing more serious symptoms in ferrets – which experience similar symptoms to humans – than other viruses.
Tests also showed that any immunity humans gain from exposure to seasonal flu does not provide protection from G4.
Already one-in-10 people who worked with pigs in China are said to have contracted G4.
Professor James Wood, who is an infectious diseases expert at the UK's Cambridge University, said G4's discovery highlighted the ease at which viruses can jump the species barrier.
"The work comes as a salutary reminder that we are constantly at risk of new emergence of zoonotic pathogens and that farmed animals, with which humans have greater contact than with wildlife, may act as the source for important pandemic viruses."
Professor Esther Choo, an American emergency physician and US science communicator, warned in a tweet: "2020 may not be done with us yet."
Professor Choo quoted a colleague, an infectious diseases expert, as saying: "I rarely get worried, but this one bears close watching. This flu strain is very, very dangerous."
However, while G4 certainly has the capability of being our next pandemic, other scientists have said it had yet to reach that stage – and may never.
Carl Bergstrom, a biologist at the University of Washington, said: "There's no evidence that G4 is circulating in humans, despite five years of extensive exposure. That's the key context to keep in mind," he said on Twitter.
That's not to say it won't. Viruses are constantly in flux and G4 could, at some point, mutate into a virus transmissible to humans.
"It is of concern that human infection of G4 virus will further human adaptation and increase the risk of a human pandemic," the researchers wrote.
The authors called for urgent measures to monitor people working with pigs.
URGED NOT TO 'OVEREACT'
Chinese Foreign Ministry spokesman Zhao Lijian told a daily news conference on Tuesday that China was closely following G4 developments.
"We will take all necessary measures to prevent the spread and outbreak of any virus," he said.
China's Global Times newspaper, seen as a mouthpiece for the ruling Communist party, played down the threat urging the public not to "overreact".
It claimed that the H1N1 swine flu pandemic of 2009 was predicted to infect 600 million people but was only contracted by 60 million.
However, the US Centres for Disease Control and Protection (CDC) has estimated 60 million people were infected in America alone. By some estimates more than 1 billion people worldwide contracted H1N1 and more than half a million may have died.
The Global Times said a veterinary medicine expert "close to the G4 research team" said the new virus was similar to swine flu and was "preventable".
The unnamed person said while G4 had the potential to jump to humans, "the chance of human-to-human transmission is minor".