Genes from a flu strain created in a lab in 1940 have been found in samples taken from pigs in South Korea, a US biologist claims.

Data from the flu virus samples were put last October in GenBank, the public database of genetic sequence information, by researchers at Chungnam National University in Daejon, South Korea.

In December, the biologist Henry Niman of Recombinomics, a biotechnology company in Pittsburgh, Pennsylvania, examined the data as part of an analysis of flu sequences. He concluded that the samples contained genes from a strain of human flu virus that was created decades ago by scientists experimenting with the virus that caused the global flu pandemic of 1918.

Neither the World Health Organization (WHO), which coordinates the international response to flu, nor the South Korean government have commented on the claim. But Laurie Garrett, a former journalist and analyst at the Council on Foreign Relations in New York, says that the WHO attributes the sequence to an error at the lab that deposited the information.

Sang Heui Seo, one of the Korean researchers, says he is unable to comment yet, adding that “further confirmation” of the sequence “is under way at this moment”.

The incident raises worrying questions about how the human flu genes got into a virus in a pig, says Niman. It could have happened naturally or in a lab accident — but it could also have resulted from experiments to produce a more deadly flu. “It could be bioterrorism,” he says.

Niman says that the flu sequences posted on GenBank contain genes from a human strain called WSN/33, which was created in 1940 in a London lab. The strain was derived from a 1933 virus related to the one that caused the 1918 pandemic, and most people's immune systems have never been exposed to anything like it. The strain could be devastating if it infected people today, he adds.

Garrett thinks that even if there was a lab error, the episode should still ring alarm bells. Without a robust, global disease-surveillance network, she says, it is impossible to confirm the WHO's view that the sequence is a mistake. The discovery of the mystery strain “reveals critical weaknesses in our global security system”, she contends.