A deadly strain of bird flu, known as H7N9, could infect the world but Chinese authorities have refused requests for lab samples from both the UK and the US.
Health bosses are worried that without a sample of the virus, the UK will struggle to create a vaccine.
Professor Ian Jones, an expert in virology at the University of Reading, said: “If the virus is going to jump you want to be ahead of the game with a vaccine.
“If the virus were to jump it would become a pandemic strain.”
H7N9 is thought to be only a few mutations away from being able to spread from humans to humans, The Telegraph reported.
At the moment it can only be spread from birds to humans.
This means a person has to come into contact with infected birds to be infected with the disease.
China has given no reason for its refusal to provide samples and experts are unsure of the motivations.
It is not known if the last H7N9 sample shared by China in 2016 is up to date enough in order to make a vaccine against newer forms.
There have been 1,625 cases of the H7N9 virus in people, so far, and some 623 people have died.
Most people who develop infections from H7N9 become severely ill.
There is up to a 40 per cent rate of cases resulting in death.
Director of the Worldwide Influenza Centre in London, Dr John McCauley, said while vaccines could also be created using available gene sequences of H7N9, vaccines tend to be developed using the virus itself.
He said: “With the gene sequence data you can develop a vaccine – it’s doable. But it’s not the way vaccines are made and regulated at present.
“There is a better feeling of confidence with the actual virus in hand.”
Infectious disease specialist at Harvard Medical School, Dr. Michael Callahan, told The New York Times: “Jeopardizing US access to foreign pathogens and therapies to counter them undermines our nation’s ability to protect against infections which can spread globally within days.”
H7N9 has been prevalent since 2013.
Experts believe it could be as lethal as the 1918 Spanish Flu which killed up to 100million people.