The US has seen foreign spy agencies carry out reconnaissance of research into a coronavirus vaccine, a senior US intelligence official has told the BBC.
Bill Evanina, director of the National Counterintelligence and Security Center, said the US government had warned medical research organisations of the risks.
But he would not say whether there had been confirmed cases of stolen data.
UK security sources says they have also seen similar activity.
An international race is on to find a vaccine for Covid-19.
Researchers, companies and governments are all involved. And their efforts are simultaneously being protected by domestic spy agencies, while being targeted by foreign ones.
Mr Evanina’s organisation provides advice on countering the work of foreign intelligence agencies to the US government, businesses and academia.
“We have been working with our industry and government folk here very closely to ensure they are protecting all the research and data as best they can,” he said.
“We have every expectation that foreign intelligence services, to include the Chinese Communist Party, will attempt to obtain what we are making here.”
The US government is trying to aid work on a vaccine with a programme reportedly called Operation Warp Speed.
Whichever country discovers the first effective and safe formulation may be able to ensure its citizens are first to benefit.
“We’ve been in contact with every medical research organisation that is doing the research to be very, very vigilant,” Mr Evanina added.
“In today’s world there is nothing more valuable or worth stealing than any kind of biomedical research that is going to help with a coronavirus vaccine.”