Virologists in China have published a paper detailing how they created more than 100 hybrid viruses from H5N1 and the H1N1 strain that caused the deadly swine flu pandemic of 2009. The virologists wanted to see if any combinations would transmit between mammals—five did.

The study, published in the journal Science, comes exactly a year after the release of a controversial paper describing how the H5N1 bird flu could theoretically be modified to become human-contagious. At that time, the international community had called for a moratorium on similar research because of threats related to the virus escaping or the information being used for deadly purposes. Various outbreaks of H1N1 have, over the years, proven extremely dangerous. However, researchers argue we need to learn more about how these viruses mutate, and indeed how hybrids form in nature, to better tackle any future outbreaks.

The process by which hybrids form is known as reassortment, and it occurs when an individual is infected with two different strains. Genetic information is exchanged across the two to form a new and unique virus, exactly what happened in 2009 when a combination of different swine, avian, and human flus from across the globe merged. H1N1 in particular seems to reassort more readily and is highly infectious among humans. On the other hand, H5N1 (bird flu) is not typically infectious. The premise behind the study was to see if hybrids could create a more infectious strain of H5N1.

According to a report by Nature, the team, led by Hualan Chen of the Harbin Veterinary Research Institute of the Chinese Academy of Sciences, created 127 different reassortment viruses by mixing seven specific chunks of genetic information from both H5N1 and H1N1. They then directly infected mice with the virus and tested 19 of the different reassortments on guinea pigs. After leaving infected guinea pigs in cages alongside uninfected ones, the team found that "the H5N1 hybrid viruses bearing one or more of the PA, NA, M, or NS genes of 2009/H1N1 were transmissible" through the air. This, they say, demonstrates that H5N1 has the potential to be transferred between humans.

"Since the internal genes of these reassortants can already replicate efficiently in mammalian hosts, we predict that similar reassortants could infect humans and subsequently acquire mutations that improve binding efficacy."

It's worth noting that guinea pigs, though mammals, contain both avian and mammalian receptors. The results would be far different in humans. Furthermore, none of the guinea pigs died, but some mice directly infected with the viruses did. It's also important to acknowledge that Chen carried out the research prior to when the moratorium was put in place.

Yet despite this, the argument that we should be prepared for all kinds of natural reassortment, the fact that the study was carried out in China's high-security National Avian Influenza Reference Laboratory at Harbin Veterinary Research Institute (biosafety level 3), and the fact that China—which is currently experiencing a deadly outbreak of the H7N9 bird flu strain—is all too well aware of the potential dangers, critics have already come out to slam the researchers for being "appallingly irresponsible" and "driven by blind ambition."

The critiques were the focus of a piece on the study by the Independent Friday, in which Robert May, formerly chief scientific advisor to the government, came out with the aforementioned harsh responses. "The record of containment in labs like this is not reassuring," he continued. "They are taking it upon themselves to create human-to-human transmission of very dangerous viruses. It's appallingly irresponsible."

Also speaking to the Independent, virologist Simon Wain-Hobson of the Pasteur Institute in Paris commented: "It's a fabulous piece of virology by the Chinese group and it's very impressive, but they haven't been thinking clearly about what they are doing. It's very worrying. The virological basis of this work is not strong. It is of no use for vaccine development and the benefit in terms of surveillance for new flu viruses is oversold." Wain-Hobson may be referring to the fact that the study was done on guinea pigs, not the ideal stand in for a human study. The Chinese team was, however, apparently planning on trialing the viruses on ferrets, which would help represent a closer model for human flu.

Back in 2009 shortly after the outbreak of the reassorted H1N1 virus, the US Centers for Disease Control and Prevention mixed the H1N1 and H5N1 virus, so Chen is far from the first to attempt this. Not only that, the US study was done with ferrets.

Andrew Pekosz, a virologist at Johns Hopkins Bloomberg School of Public Health, told CIDRAP News that he sees work like the Chinese team's as essential: "The more we understand how wide-ranging those combinations of genetic changes are that can lead to this kind of transmission, the better off we'll be. That knowledge helps inform us what we should be looking for regarding viruses that are potential human pathogens."

Pekosz added that he believed, from what he knew, the team took all safety concerns into account at the same standard as a US lab. He also pointed out that there's no way we can know if the same reassortments would ever naturally occur.

It does seem, however, that the lifting of the moratorium does not sit well with many in the community.

This story originally appeared in Wired UK.