Experts are concerned that a new strain of bird flu has the potential to become a pandemic.
The H10N8 virus has already killed one woman in China after visiting a live poultry market, however researchers are not sure if this was the source of the infection.
Since then, a second person has been infected. Scientists have told The Lancet that the potential for this to become a pandemic “should not be underestimated”.
There is no evidence that H10N8 can spread from human to human, however, there is concern that is could evolve to do so.
Dr Jeremy Farrar, director of the Wellcome Trust, told the BBC: "We should always be worried when viruses cross the species barrier from birds or animals to humans as it is very unlikely that we will have prior immunity to protect us.
"We should be especially worried when those viruses show characteristics that suggest they have the capacity to replicate easily or to be virulent or resistant to drugs. This virus ticks several of these boxes and therefore is a cause for concern."
An outbreak of a similar influenza virus called H7N9 has already killed a quarter of those infected in China and has recently reached Hong Kong and Taiwan.
Dr John McCauley, director of the World Health Organization Collaborating Centre for Influenza said: "This case reminds us to be aware of human infections from animal influenza viruses, like the H7N9 cases in China which increase daily. Previously we did not think that H7N9 infections might be so lethal. Now we also must consider H10N8 infections as well."